Do Eating Carbs Really Make You Fat?

If you were to ask 100 dieters whether carbohydrates were good for them or bad for them how many do you think are going to say bad?  I’m willing to wager that at least 90 out of 100 people will tell you that carbs are bad for them.  If asked to elaborate why carbs are bad, a common response is that carbs are bad because they make you fat.


American’s relationship with carbohydrates has gotten so bad that when carbs are brought up our default answer is, carbs are bad.  Context does not matter.  The fact that there are thousands of different types of carb containing foods does not matter.  Starchy vegetables?  Bad.  Fruit?  Bad.  Beans?  Bad.  Bread?  Why are you even asking, bad!


We are now taught or at least lead to believe that carbs caused obesity, eating carbohydrates will make you fat, removing carbohydrates will cause you to lose weight, and fat and protein are good for you.  But here’s the thing.  The topic of carbohydrates is far more nuanced than anyone wants to admit or has the time to learn about and each of these beliefs needs to be examined independently.  For example,


Did eating carbs make you fat? and Do eating carbs make you fat? are distinctly different, time-dependent (past versus future) questions with distinctly different answers but are often lumped together in the same argument: carbohydrates make you fat.


Let’s start with Did eating carbs make you fat?  This question is impossible to answer but there are many people who are willing not just to say yes but to EMPHATICALLY SAY YES!  Without being able to go back into time and run randomized controlled experiments (i.e. make some people eat more carbs and other people eat more fat) we’ll never know.  What we are left with are retrospective analyses of questionnaire data.  Each year since 1970, the United States Department of Agriculture’s (USDA) Economic Research Service (ERS) has asked Americans to fill out a survey on what they eat and how much they eat.


They have then been able to categorize what Americans ate into seven categories

·      Added plant-based fats and oils

·      Added sugars and sweeteners

·      Dairy

·      Fruit

·      Grains

·      Meat, eggs, and nuts

·      Vegetables

And from these analyses have been able to show trends in what Americans consumed over the years and decades since (if you are interested in nutritional trends, this is an amazingly rich database).  Starting in 1962 we have also been tracking the prevalence of obesity (body mass index; BMI > 30).  From these data we can establish correlations between the foods we eat and the prevalence of obesity (Figure 3) but we cannot establish cause and effect.  The best we can do is offer an educated guess as to what happened but we cannot draw any definitive conclusions (but don’t tell low-carb advocates that).

Do eating carbs make you fat? is a question that can be answered but would require a large scale randomized controlled trial performed over the course of months, years, and decades.  This trial would be extremely costly to run and also a logistical nightmare.  In a nutshell, you would have to provide high carbohydrate diets to thousands of people and high fat diets to thousands of other people.  Sounds pretty easy, until you think about the fact that you will not just be providing recommendations but you will be providing the food itself and trying to control for other behaviors such as exercise or workplace activity (i.e. an accountant versus a steel worker).  I don’t know about your family but my wife and I easily spend $500/month on groceries.  And this doesn’t even consider the technical staff you would need to run the study or the fact that in pre-Covid-19 times that people were able to eat out more frequently.

So with all that being said, we have controlled feeding studies over the course of several weeks but due to subject burden and research cost, we also have not been able to answer the question of whether or not eating carbs make you fat.

The third question we should be asking is “If I reduce or remove carbohydrates from my diet, will I lose weight?”  The short answer is yes, in the short-term but probably not in the long term.  So how has the myth of carbohydrates making us fat become so maddeningly engrained in our society if the evidence supporting it is so shaky?

In this article I want to lay out why I do not believe that eating carbohydrates cause you to become fat nor do I believe that removing carbohydrates from your diet will cause you to lose weight.  We don’t have the time in this article to address the full history of the anti-carbohydrate movement and I know that your attention span is short so I will do my best to highlight what I feel are the most important points.  For a brief history on carbohydrates and fad diets I would refer you to an article that my intern, Julie Kent MS, RD, wrote on Why We Villainize Carbohydrates.

The Myth that Carbohydrates Caused Obesity

There is a deeply engrained belief among the dieting population (which happens to be most of us) that carbohydrates caused obesity.  If carbohydrates caused obesity, then by logical extension the cure for obesity must be removing the cause (carbohydrates).  You don’t have to search the internet very hard and you’ll find all kinds of evidence supporting carbohydrates causing obesity such as the graph that I created below (Figure 1).

Figure 1. Carbohydrate Consumption has Drastically Increased in the past 40 Years.  Source: United States Department of Agriculture Economic Research Service’s Food Availability (Per Capita) Data System.  Carbohydrate calories/day was calculated by combining the category of added sugars and sweeteners with grains.

Between 1980 and 2000 carbohydrate calories increased by 245.7 calories/day.  While it is true that carbohydrate consumption has greatly increased over the past 40 years, so has dietary fat intake (Figure 2). 

Figure 2. Dietary Fat Intake has Greatly Increased over the past 40 Years.  Source: United States Department of Agriculture Economic Research Service’s Food Availability (Per Capita) Data System.  Fat calories/day was calculated from the Added plant-based fats and oils category.  The meat eggs, and nuts category was left out of this comparison because these food sources also contain large amounts of protein and the fat to protein ratio is not easily discerned.

Between 1980 and 2000 calories from fat in the diet increased by 173 calories/day.  So it is negligent to blame carbs but not fat.  Carbohydrate isn’t solely to blame and dietary fat isn’t solely to blame.  They are both to blame (Figure 3).

Figure 3. The Relationship between Daily Calorie Intake and the Prevalence of Obesity.  The increase in calories/day is directly proportional to the increase in the prevalence of obesity.  Source: United States Department of Agriculture Economic Research Service’s Food Availability (Per Capita) Data System. 

The increase in daily calorie consumption directly mirrors the increase in obesity.  As the number of calories/day consumed increased, so did the prevalence of obesity.  If we look back to the year 1980, Americans consumed 2083.6 calories/day, which increased to 2402.5 calories/day by 1994 and peaked in 2002 to 2588.8 calories/day before leveling off.  It just doesn’t make any sense to focus only on carbohydrates and ignore fat’s role in increasing the number of calories in our diets…that is unless you’re trying to sell people a low-carbohydrate diet.

Why Low-Carbohydrate Diets are So Appealing?

If total calorie intake caused obesity (not carbohydrates per se), why are we so resistant to reducing our total calorie intake (carbs, fats, and proteins) rather than focusing only on carbohydrates?  If it is all about calories, why do we single out carbohydrates?  While this makes no sense to me, I have thought long and hard about this question and this is what I’ve come up with.

1.     People crave simplicity and direction: fad diets in general but low-carbohydrate diets in particular offer a binary, yes or no, black and white system of eating.  You only need to follow one rule.  Are carbohydrates in that food?  Then you can’t eat it. Done.  Traditional dietary advice is far more nuanced and difficult to follow.


2.     Eliminating carbohydrates is the lowest hanging fruit: carbohydrates make up approximately 50% of the calories in an American diet (fat makes up 34%, protein 16%).  So if losing weight is all about calories, it makes sense to reduce the number of calories from the greatest calorie contributor, carbohydrates.


3.     People cannot control themselves: many people are self-described carbohydrate addicts.  But have you ever heard of a fat addict or a protein addict?  I haven’t.  So many people report that they crave carbohydrates and that they cannot stop themselves from eating them.  So what better way to stop yourself from eating them, then to not eat them at all.  Again, this doesn’t make a whole lot of sense to me since there are so many types of carbohydrates and I’m not sure why we can’t identify our “problem carbs” and avoid them rather than eliminating all carbs.  I once assigned an intern to write an article answering the following question, if carbs are so addictive, are bananas a gateway drug?  Unfortunately our rotation ended before we could answer this question.


4.     Dietary restriction hasn’t worked in the past: traditional dietary advice promotes calorie restriction by controlling your portion sizes and eating lean meats.  The vast majority of the people following this advice fail to lose weight and keep it off.  If cutting total calories didn’t work, what else is there to do?  Carbohydrate restriction is oftentimes the next step in their journey.


5.     Low-carbohydrate diets allow you to eat foods you like: traditional weight loss diets of salads and chicken breast are bland and overly restrictive.  A big selling point of low-carbohydrate diets is that you can still eat many of the things you love (i.e. meats, cheese, butter).  Traditional weight loss diets don’t allow you to eat anything that you like (or at least that is the perception) and leave the dieter feeling deprived.  There is only so long that you can go on eating with little to no pleasure before you are going to break and go back to eating foods that give you pleasure.


6.     Carbohydrates are not essential to the diet: nutrients “essential” to the human body must be obtained in the diet because the human body cannot manufacture them.  Although the body (brain and spinal cord) prefers blood glucose (usually obtained from carbohydrates) and the red blood cell must use carbohydrate as a fuel (they cannot use fats or proteins) carbohydrates are not essential to the diet (the body can manufacture blood glucose) whereas there are 9 essential amino acids and there are essential fatty acids (i.e. omega 3 & 6).  One could argue that this is a higher level selling point and not on the minds of most dieters but one can argue that you technically do not need to eat carbohydrates to stay alive or be healthy.


7.     Food sources containing fat AND carbohydrate are now off limits: by restricting foods that contain both fat and carbohydrate you’re now reducing both your fat intake and your carbohydrate intake.  Foods containing fat AND carbohydrate are some of the best tasting (and difficult to not eat them/stop eating them) and they are also calorie dense (contain lots of calories in a small portion).  By eliminating carbohydrates you are also eliminating many of these problem foods.


8.     Low-carbohydrate diets reduce the amount of processed food in the diet: many of the high fat food sources available to us are also minimally processed.  This is another clever way of getting people to eat fewer potato chips, cookies, cakes, and candies than they otherwise might sneak into their diets.  Plant based (carbohydrate) advocates can argue that they offer a simple rule to eating less processed foods as well – can you pick the food off a tree, pull it from the ground or easily trace its origins?  This is another pretty simple method of determining whether a food is on the “good” list or the “naughty” list but it isn’t as easy as the yes or no binary system of does it contain carbs or not?


9.     Fat and carbohydrate promote the feelings of fullness: if you reduce the number of calories you typically eat, you are going to feel hungry.  Low-carbohydrate diet advocates will claim that eating protein and fat promotes the feeling of fullness (satiety) while carbohydrate generally does not (with the exception of dietary fiber).  Although I am not super well versed in this research area (satiety) I have always had trouble believing that this matters all that much.  Does fat and protein promote satiety, yes, probably, but does it promote satiety to the point where you won’t be craving more calories while in a calorie deficit?  I don’t believe so.  To me this is another failure of quantification where the return on your investment is far lower than what is being promoted and sold to you.  Why we eat what we do and how much we eat what we do is much more complex than whether you’re eating enough fat, protein and/or fiber.  Does the feeling of fullness prevent eating?  Does hunger drive all eating occasions?   I think not.  You can argue that every little thing helps but as I have pointed out before, this “small changes” type of thinking is not sufficient to cause the large scale change that most people are looking for.


10.  Eating fat makes you burn more fat: there is a commonly held belief (myth) that to burn more fat you need to eat more fat.  This is only partially true.  Energy balance and the availability of carbohydrate in the diet controls fat burning.  Eating fat does not control fat burning.  The bottom line is carbohydrates control fat burning.  As we will see later on in this post, removing carbohydrate from your diet removes one of the brakes on fat burning.  If you don’t have any carbohydrate to burn through you will immediately start burning fat as a fuel source.  That’s great and all but if your diet is higher in fat, then you are also adding more fat into the system (your body) and now the body is going to burn dietary fat AND stored body fat.  Conversely if you eat a high carbohydrate diet low in fat, now you have to burn through those carbohydrates to get to the stored body fat but you’re also not adding much dietary fat into the system (you are eating a low-fat diet) so when the body does burn fat it can burn stored body fat rather than ingested body fat.  Both low-carbohydrate/high fat diets and high-carbohydrate/low-fat diets work in the same fashion, through creating a negative energy balance.  The idea that eating more fat makes you burn more fat is misguided.


11.  It is impossible to eat too many calories when cutting out carbohydrate: while I don’t exactly agree with this statement, this is a common claim.  There are far, far more carbohydrate sources/types/varieties than there are fat sources and as we saw in bullet point 2, the typical diet contains far more carbohydrates than it does fat.   I’ve been told (by the corporate Atkins people) that you will get tired of eating the same fat sources again and again and again before you reach a positive energy balance, therefore, the lack of variety in the diet will cause you to lose weight.  They are deeply hypocritical because they will also tell you, the public, that they have thousands of Atkins friendly recipes.  You can’t have it both ways.

There are a number of other proposed benefits of a low-carbohydrate diet over a moderate or high carbohydrate diet, namely that a low-carbohydrate diet is the diet of our ancestors, that the United States Department of Agriculture (USDA’s) recommendations are highly flawed and biased, and that a low-carbohydrate diet will better control blood sugar, reduce your risk of developing diabetes, and reduce your hunger.  While there is some truth to each of these claims, in and off themselves, they are sensationalized to sell you low-carbohydrate diets.


With all that being said, there are clearly a number of potential benefits to adopting a low-carbohydrate diet that contain at least some merit.  So what’s the big deal?  Why am I so irritated by low-carbohydrate diets?  If they work, they work, right?  Well, that’s the problem.  They don’t really work in the long term any better than any other diet and in my opinion are built on a series of lies and misunderstandings of metabolism.

Do Low-Carbohydrate Diets Work?

Every single diet out there that restricts calories can work for some people, work great for others, and not at all for most (Figure 4).

Figure 4. The Individual Response to Any Given Diet Varies Considerably.  Each dot represents an individual’s response to one of four diet conditions, Atkins, Weight Watchers, Slim Fast or No Diet (Control Group).  While some individuals lose a considerable amount of weight, others lose no weight, and some even gain weight. Taken together, no diet is better than another diet. Data adapted from Truby H; BMJ, 2006.

For example, in a study by Truby et al; 2006, individuals were assigned to one of four diet conditions, Atkins, Weight Watchers, Slim Fast or No Diet (Control).  In Figure 4 each individual bubble represents one individual’s weight change on their given diet.  As you can see, some people lost a tremendous amount of weight, most people lost at least some weight, and some people actually gained weight.

This study provides a great comparison between a low-carbohydrate diet (Atkins), a calorie restricted diet limiting carbs and fats (Weight Watchers), and a diet containing meal replacements (Slim Fast).  The temptation in interpreting these data are to deduce that if people were to find the “right diet” for them, that they would all be successful.  That just because Atkins might not have worked, that perhaps Weight Watchers would.  This is wishful thinking.  The people who are going to be successful are going to be successful no matter the diet type and those that aren’t successful will not be successful regardless of the diet type.  Although we’re not going to get into it here, some research has shown that people tend to be more successful (albeit not by that much) on diets that are randomly assigned to them than they are on diets they get to choose on their own.

Another common argument that needs to be addressed is that some researchers have found, through a meta-analysis, that low-carbohydrate diets are superior to low-fat diets in terms of weight loss.  That’s all fine and good but let me explain this to you.  A meta-analysis is a collection of research papers in which they take all of the data from the individual papers and do one big analysis on them.  By pooling together this separate data they can draw more powerful conclusions than any one individual paper can provide.  There are several meta-analysis papers out there that have shown that low-carbohydrate diets are significantly (according to statistics) superior to low-fat diets.  And low-carbohydrate advocates just LOVE THIS! 

But they are missing the point.  There is a difference between statistical significance and meaningfulness that I learned as a masters student.  Something can be mathematically (statistically) different but meaningless in real life.    If people on a low-carbohydrate diet lost 9 pounds and people on the low-fat diet lost 6.5 pounds, one could say that the low-carbohydrate diet is superior by way of statistics.  But my point is that whether you lose 9 pounds or whether you lose 6.5 pounds, you are going to be disappointed if your goal was to lose 50 pounds! 

I’m sorry but these results simply are not good enough.  It’s like saying my 4-12 football team beat your 3-13 football team.  Both teams stink and although they have bragging rights for one day, a 4-12 season is an utter failure and should not be touted as a success.  In fact, your coach needs to be fired and your roster needs to be overhauled.  Stop celebrating failure and touting the few success stories.  Touting the individual success stories is great.  Players who had a good season on a losing team should be celebrated.  But we shouldn’t celebrate the bad team, yet that is exactly what low-carbohydrate advocates do to sell their diets.

At The Science of Dieting, we have downloaded and categorized 1500+ research papers and have found little to no evidence supporting the superiority of low-carbohydrate diets for weight loss over the course of time (greater than six months) compared to other dietary interventions (i.e. calorie restriction, low-fat, vegetarian, alternate day fasting, etc.).  We went to the extreme lengths of downloading and categorizing the entirety of the weight loss literature because we were sick and tired of people cherry picking evidence to support their dietary approach.  They all suck.  None of them are good. 

Our initial goal was to create a database of papers and to share that database and the papers so that we could tell the low-carbohydrate (and fad diet advocates) that we’ve done your homework for you and that you can no longer cherry pick your evidence.  You need to look at the entirety of the literature not just the papers that support your narrow view of dieting.  But before we did that we received legal counsel that we would soon be in court for copyright infringement by sharing papers that we did not own or create.

Rather than saying, all diets suck, none of them are good and leaving the conversation, we thought we would put our money where our mouth is and design a program that, based on the scientific literature, would give you the greatest chance of success.  Eventually, we hope to be able to show you the data and the graphs supporting our conclusions but as you can understand, this is a massive undertaking and we do not have the staff to do this at this time.

But to answer the question, “do low-carbohydrate diets work?”.  Yes, in the short-term, not in the long-term, the amount of weight you lose will likely be lower than you wish to lose, and they are no better than the other dietary interventions out there (low-fat, alternate day fasting, vegetarian, high protein, etc.).

Why Do Low-Carbohydrate Diets (and Diets in General) Fail?

There are tens and hundreds and thousands of reasons why diets fail.  Many of the reasons why low-carbohydrate diets fail are the same reasons why any diet fails, because they are not sustainable over time.  They are not compatible with real life and the food environment challenges you face on a day-to-day basis.  If you read the academic literature, scientists who study weight loss will report that dietary adherence (how well you can stick to a diet) is the number one predictor of how much weight you will lose and how much weight you will keep off.  Not carbs, not protein, not fat, not ketosis, not any of that.  Adherence.

It doesn’t matter how simple your rules are (i.e. don’t eat carbs), if you are continually exposed to carbohydrates your dietary adherence is going to slip.  In the weight loss world there is no herd immunity.  Just because you are trying to protect yourself from carbohydrates doesn’t mean that other people are too.  Carbohydrates are a fact of life and are going to slip back into your diet whether you want them to or not.

I’m doing my best not to make this article about selling you The Science of Dieting’s weight loss program (Todd’s 12 Steps to Healthy Eating) but it is difficult not to make these comparisons.  Todd’s 12 Steps to Healthy Eating focuses on controlling your food environment and not on the food itself.  Too many of our dietary approaches to weight loss attempt to manipulate the macronutrient ratios (ratio of carbs, fats, and proteins) or try to control calories (traditional advice) and do not spend nearly enough time on trying to control your food environment (access to ultra-processed highly palatable food through meal planning).

Instead of focusing on carbohydrates I think we should focus on the three ways in which we consume too many calories

1.     Food Frequency: how often you eat

2.     Portion Sizes: how much you eat in one sitting

3.     Calorie Density: how many calories are packed into a given quantity of food or drink

These are the three ways you can consume too many calories.  There are no other ways of overeating.  They will all fit into food frequency, portion sizes or calorie density.  If you can set up your food environment to control these three factors you will be successful.  I (almost) guarantee it.


There is a debate as to whether food quantity, food quality, or both are primarily responsible for weight gain.  The answer, of course, is all of the above.  If you eat high quality food (i.e. Chipotle brags about high quality, fresh ingredients) but if you eat too much of it (portion size), you are going to gain weight.  If you eat ultra-processed highly palatable food you are not only eating lots of calories but it is going to be very difficult to stop eating that food once you have started (i.e. Pringles, once you pop you can’t stop) (food frequency and calorie density).


Instead of having this idiotic fight among health professionals and health enthusiasts and fighting a war that nobody is going to win and frankly does not matter, we need to take the focus off the food and place our focus on the individual and the food environment that he or she lives and works in.  Even if carbohydrates did cause obesity, removing them does not cure obesity.  We need to stop having this argument because it is a distraction from what matters, controlling your food environment.

Carbohydrates Causing Obesity Does Not Make Metabolic Sense

The idea that eating carbohydrates makes you fat does not make any metabolic sense.  Yes, carbohydrates can make you fat when eaten in excess (i.e. more calories than you burn) but eating too much fat (i.e. more calories than you burn) will also cause you to become fat.  Fat doesn’t get a free pass just because carbohydrates might contribute slightly more daily calories.  I can’t even begin to try to explain the idea that carbohydrates, per se, makes you fat because there is no basis to even start the discussion from.  If you ask a dieter how carbohydrates make them fat, they will answer, “They just do” or “all I know is that when I eat carbs I get fat”.  But what does that even mean?!


I know that people will cite the insulin/fat hypothesis whereby eating carbohydrates spikes your blood sugar, which in turn causes an insulin spike.  Insulin is an anabolic hormone that promotes fat storage and inhibits fat breakdown.  Therefore, if you’re not burning fat, you’re storing it.  This is a nice story full of convincing arguments but again, where is the long term evidence? If this were the case, then we would have strong epidemiological evidence showing that people eating lots of carbohydrate would weigh more than those that didn’t and you would also expect a dose response, where those that ate the greatest amount of carbohydrate would also weigh the most due to their excessive insulin spikes and fat burning suppression.  But this isn’t the case and all we’re left with is a theoretical story that supports people selling (or using) low-carbohydrate diets for weight loss. 


Volumes has been written about this insulin/fat hypothesis and some short term “evidence” has been produced.  I’m not taking the time to fully address this topic because I view it as a dead end waste of time.  And I like to write lengthy blog posts so that’s saying a lot.  Instead of wasting our time on a topic that may or may not be real and offers little to any real value, I would rather talk about metabolism, as I understand it, and why carbohydrates causing obesity does not make sense.


Let’s begin our discussion by asking a simple question.  If you consume more calories than you burn, what happens to those extra calories?  They turn to fat right?  No, not exactly. 


The body primarily burns fat and carbohydrate for fuels (protein accounts for less than 10% of total fuel).  We can further break down fat and carbohydrate fuel reserves into four distinct sources/stores (Figure 5).

1.     Liver glycogen (stored carbs)

2.     Muscle glycogen (stored carbs)

3.     Subcutaneous and visceral fat (fat stored under the skin and around internal organs)

4.     Intramuscular fat (fat stored within skeletal muscle)

Figure 5. Body Stores of Fuel and Energy.  The body stores a limited amount of carbohydrate as glycogen but can store an unlimited amount of fat.  Even thin people (i.e. 12% body fat) can store an ample amount of fat.

The body’s usage of these fuels is governed by the composition of the diet (ratio of carbs to fats), energy balance (positive or negative), and physical activity intensity and duration (if exercising).  There are numerous exercise physiology textbooks and research papers dedicated to delineating out the who, what, when, where, how, and why specific fuels are used in specific exercise intensities and durations.  Although I would love to tell you about this all, it is a topic for another day.

The Oxidative Hierarchy

Instead, I will give you one rule by which fuel (fat and/or carbohydrate) burning is regulated and it is known as the oxidative hierarchy.  The oxidative hierarchy states that whatever fuel your body can store the least of will be burned first, followed by the next least stored fuel, followed by the next least stored fuel and so on.

As you can see in figure 5, even if we are really skinny (12% body fat) we store WAY MORE fat than we do carbohydrate.  Due to the oxidative hierarchy (as well as other reasons not discussed here) the body tends to burn carbohydrate before it burns fat.  Carbohydrate is the preferred fuel source, fat is a backup fuel supply.  Now, of course the mixture of fuels you burn at any given time depends upon a variety of factors but on a normal, mixed diet where you are consuming similar amounts of carbs and fats, you have to burn through your carbohydrates before you can access your fat.

For carbohydrates to make you fat, you would have to eat enough carbohydrate to ensure that your body can’t burn through all of the carbohydrate to access your fat stores AND you will need to store/convert that carbohydrate into fat.  But to do this, we would also need to make sure that our glycogen stores (storage form of carbohydrate) are completely topped off in our muscle and in our liver (Figure 5).  Then, and only then, will our body choose to convert carbohydrate into fat, a process known as lipogenesis.

Luckily for us, experiments testing this premise have been performed (Figure 6).  In a study by Acheson and colleagues way back in 1988, research participants were given a low amount of carbohydrate for three consecutive days (42, 56, and 52 grams/day when the typical American consumes closer to 275 grams/day on a normal mixed diet) before giving these same research participants a sickening amount of carbohydrate in the way of over 700 grams/day and up to close to 1000 grams/day for the next seven days (Figure 6).

Figure 6. The Effect of Eating Massive Amounts of Carbohydrate on Carbohydrate Burning (Oxidation), Storage (Glycogen), and Conversion to Fat (Net De Novo Lipogenesis).  Consuming triple the amount of carbohydrate you would normally consume still does not cause the conversion of carbohydrate into lipid (fat).  Only after multiple days of a massive carbohydrate overfeeding and glycogen saturation (maximal storage capacity) is carbohydrate converted to fat.  Data adapted from Acheson, KJ; 1988 Am J Clin Nutr.

What the researchers found is that even after eating a grotesque amount of carbohydrate for one day (757 grams or 3x normal), the additional carbohydrate consumed was either burned (carbohydrate oxidation) or stored (glycogen storage).  After consuming an additional 834 grams of carbohydrate the following day, some of that carbohydrate began to be stored as fat.  The following 5 days of crazy excessive carbohydrate intake resulted in more carbohydrate burning and more conversion of carbohydrate into fat stores (lipogenesis).  It was only after glycogen stores were completely topped off that the body converted carbohydrate into lipid (fat).  If you performed exercise lowering your glycogen stores, much of that carbohydrate would be shuttled back into glycogen.


The point of this research (to me) is that it takes a massive amount of carbohydrate over the course of several days to induce the body to convert the carbs to fat and store it.  The body’s first choice is to burn carbohydrate, it’s second choice is to store carbohydrate as glycogen, it’s third and final choice, if forced to, is to convert carbohydrate to lipid. 


It should be noted that a positive energy balance (more calories consumed than burned) is required for carbohydrates to be stored as fat.  Even if you were eating nearly 100% carbohydrate, while maintaining energy balance, you’re not going to store carbohydrate as fat.


Carbohydrates do not make people fat.  Too many calories makes people fat.  The idea that carbohydrate intake caused obesity only tells part of the story…the low-carb enthusiasts conveniently leave out the fact that while carbohydrate intake increased ~245 calories/day from 1980 to 2000, the number of fat calories typically consumed/day also increased by ~173 calories.  There are many reasons for low-carbohydrate diets to be appealing to people: low carbohydrate diets offer simplicity and direction by having you follow only one rule instead of hundreds (if it contains carbs don’t eat it), allows you to eat foods you like, and helps limit the number of processed foods in your diet.  Despite these potential benefits, low-carbohydrate diets are not any more successful in long-term weight loss than low-fat diets or meal replacements.  The proposed benefits don’t translate into what matters, long-term weight loss success. 


There are a multitude of reasons why low-carbohydrate diets fail.  Many of these reasons also cause the failure of numerous other flavors of fad diets but boils down to dietary adherence.  While I am no fan of low-carbohydrate diets (see my article on the Keto diet: The Ketogenic Diet is Bullshit), I have also said for quite some time that All Diets are Created Equal(ly) BadI’m not against low-carbohydrate diets, I AM AGAINST ALL FAD DIETS and I define a fad diet as any diet that is not unique to you. 


Low-carbohydrate diets (and fad diets in general) do not make metabolic sense.  Carbohydrates do not spontaneously convert into lipid but only do so when certain conditions are present.  A positive energy balance, full glycogen stores, and repeated amounts of massive carbohydrate intake are required for a substantial conversion of carbohydrate into lipid.  Carbohydrate likely protects fat from being burned but is less likely to be converted to fat.  Low-fat/high carb diets and low-carb/high fat diets both work through creating a negative energy balance and the resultant increase in fat burning with no significant difference in the effectiveness between the two diets.


The only thing that fad diets (such as low-carbohydrate) have taught us is that they don’t work.  And in having to formulate an argument against low-carbohydrate diets I’ve found that we’re focusing too much of our effort on the specific foods we eat and not enough of our efforts on why we eat those foods in the first place (our food environments). 


As a final shameful plug, please check out The Science of Dieting’s webpage to learn more about why you, and only you can fix your diet, why you should create your own nutrition rules to fix your food environment, and why finding the right matrix of meal solutions to guide your meal planning is in my opinion, the only way to conquer weight loss once and for all. 


Do eating carbs really make you fat?  No, and let’s kill this idea once and for all.  It doesn’t deserve any more of our attention, headspace, efforts or financial considerations.  Despite some success stories, the damage done by low-carbohydrate diets on those seeking help is far worse than the few success stories that come out of the low-carb/anti-carbohydrate movement.  We’ve been there, done that.  It doesn’t work.  Let’s move on from this discussion and put it where it belongs, in our past.  I don’t want to waste any more energy talking about it and neither should you.