Is It Better to Lose Weight Fast or Slow?

Conventional wisdom for losing weight and keeping it off has been to lose weight gradually over the course of time (after all slow and steady wins the race).  The thought was that if you lost weight rapidly, that you would ruin your metabolism and consequently gain all of the weight back.  It turns out this thinking couldn’t be further from the truth.  In fact, the opposite may be true (Figure 1).

Figure 1. The Amount of Weight Lost on a Diet within the First Two Months Predicts Weight Loss for Years to Come.  Each data point from 0 to 12 months represents one month (a monthly weigh in); thereafter each data point represents one weigh in (yearly weigh in).  Data adapted from Unick, JL 2015; OBESITY.

In a study by Unick et al., 2015, weight loss participants were instructed to consume 1200 – 1800 calories/day with two meals and one snack coming from meal replacements for the first six months of their diet.   From 7 – 12 months participants replaced one meal and one snack with a meal replacement, while eating “real food” for their other meals and snacks.  All participants were encouraged to increase their physical activity to at least 175 minutes/week by 6 months.  Research participants also attended weekly behavior change meetings months 0 – 6 and three meetings/month for months 7 – 12, so it wasn’t as if they were left on their own.

What the researchers found is that those individuals who lost the most amount of weight during the first two months of their new diet (gold line; > 6% of initial body weight lost), ended up losing significantly more weight over the coming months and even years.  Individuals who lost less than 3% of their initial body mass during the first two months (blue line; < 3% of initial body weight lost) could be considered “slow and steady/gradual weight losers” whereas those who lost greater than 6% of their body mass in the first two months (gold line) would traditionally be considered rapid weight losers.  As you can see if figure 1, if you want to maximize the amount of weight you lose, you better lose as much weight as you can during the first six months of your diet.

Study after study after study shows this same effect: the amount of weight you lose and keep off is dependent upon how much weight you lose in the first 0 – 6 months, with the first two months probably being the most important.  After six months, most people will begin gaining some of their weight back.

Why Do You Gain Weight Back after Six Months?
So why do you start gaining weight back after six months?  While there are tens and hundreds of reasons, the greatest of them is dietary adherence.  When you first start a weight loss program, you are highly motivated and losing weight is at the top of your priority list.  But as time goes on, the weight loss program is less novel, becomes stale, less of a priority, and you will begin to slide back into old habits, whether this decision is made consciously or unconsciously or a mixture of both is debatable.  That’s just human nature.  You can’t expect to keep up that type of laser focus forever, irrespective of what you are trying to accomplish.  You’re going to need a break.  That’s one of the reasons The Science of Dieting and Phoenix Fitness recommends

    1. Controlling Your Food Environment
    2. Dieting as Hard as You can for 0-6 Months Before Taking an Extended Dieting Break

It sounds overly simplistic but if the food isn’t available to you, you can’t eat it.  This is why it is important to control your access to ultra-processed, highly palatable, high-calorie food.  Think about the places you eat.  They probably involve work, home, eating out, and potentially school.  To the best of your abilities and level of control, creating a food environment that eliminates or at least limits the number of opportunities to eat ultra-processed, highly palatable, high-calorie food (temptations) will help you keep your number of daily calories down.  At The Science of Dieting, we are in the process of developing an entire course devoted to helping you control your food environment and keeping your calories down called Todd’s 12 Steps to Healthy Eating, a program named after our founder, Todd M. Weber PhD, RD.

We also recommend dieting as hard as you can for the first 0-6 months of a weight loss program before taking an extended break.  It is extremely challenging to consume a low calorie (800 – 1200) or very low calorie (< 800) diet for more than a few months due to the severity of their restriction.  Most adults, depending on body size and activity level will require between 1800 – 3000 calories/day, so you can see that this is quite a restriction.  After a month or two of eating meal replacements and tv dinners, the staleness of your diet, your hunger, and your biology will drive you to want to eat more calories and real food.

But What if You Haven’t Lost All the Weight You Wanted to Lose?
The temptation is to try to struggle through the hunger and continue attempting to eat a low calorie diet.  What tends to happen is that you a) aren’t very good at keeping your calories low and b) you are miserable from having to eat so few calories and the same types of foods over and over and over again (weight loss companies will tout their 1000 recipes and meal replacement types but give me a break, this isn’t the same as eating real food).  So not only are you not losing weight but you’re also miserable attempting to do so.  This double negative is not good for your mind or your body.

The other temptation is to take a short break and then go back on the low calorie or very low calorie diet.  But this doesn’t seem to be a great strategy as the amount of weight you will lose on your second low calorie attempt will likely not nearly be as much as you lost on your first attempt (Figure 2).

Figure 2. Weight Loss Dramatically Decreases with Successive Weight Loss Attempts.  Participants consumed 500 calories/day for 0 – 3 months, 1500 calories/day for 3 – 6 months, and 500 calories/day for 6 – 10 months.  Data adapted from Smith & Wing, 1991; HEALTH PSYCHOL.

In a classic study by Smith & Wing, 1991, research participants were asked to consume 500 calories/day for 3 months.  Knowing that it is extremely difficult to stay on such a restrictive diet (and the fact that people still need to lose more weight after the three month intervention), the researchers gave the dieters a break for 3 months by allowing them to consume roughly 1500 calories/day before reinitiating a 500 calorie/day diet for months 6 – 10.  As you can see in figure 2, despite being instructed to eat only 500 calories/day, the research participants lost nearly no weight during their second very low calorie diet attempt.  They underwent a whole lot of pain for essentially no gain (adherence to the 500 calorie advice was significantly lower the second time around).

Although there are thousands of factors that go into losing or gaining weight, you can broadly categorize these factors into either physiological or behavioral categories.  Physiological factors are those biological factors within your body (i.e. your metabolism) whereas behavioral factors are the decisions that you as a free living human choose to make.  It appears that behavioral, rather than physiological factors lead to the decreased weight loss during the second very low calorie bout (6 – 10 month period).  And in general most research supports this conclusion, that yes, physiology can and does change in individuals, but that behavioral factors may play a more significant impact on weight loss or weight gain than biology per se.  In plain English, this means that your metabolic rate didn’t decrease more than we would expect it to during your weight loss journey and if you were able to actually eat 500 calories (stick to the diet; dietary adherence; behavior) that you would indeed still lose weight.  But most people cannot tolerate that level of restriction for that long.

People will argue with me by saying that physiology is behavior (brain cell physiology causes/controls behavior).  And they’re right.  I’m making a distinction between physiology and behavior because in general, physiology is very difficult to change and control, whereas behaviors can be more easily managed (although it is still extremely difficult to control, it is doable).  If we secede all control by blaming physiology, then we are certainly going to lose the behavior battle as you’re going to say, well, it’s out of my control, what can I do about it.  But if we metaphorically treat these as two different categories, we may be empowered by having some sense of control.

Yo-Yo Dieting and Weight Loss
Research also seems to show that serial (yo-yo) dieters, those who have completed numerous diets or weight loss programs tend to lose less weight than individuals trying their very first diet program.  And I don’t believe this is because yo-yo dieters have ruined their metabolism.  Rather, I believe that dietary adherence (behavioral factors) is not as strong the second, and third, and fourth time you have tried dieting to lose weight.  I mean think about.  If you have tried to lose weight and have failed numerous times, it is very difficult to convince yourself that this time is going to be any better.  And you’re more likely going to let a few more things slide, rather than strictly following the diet.  As many times as you tell yourself that “this time is going to be different” there is still that little voice in the back of your head that is telling you that in your heart of hearts, you know you’re going to fail even before you start.  You may not want to admit it, but it’s there.  You want to change but you can’t and all of your previous failures feel like a giant weight that is dragging you down.

There is absolutely no doubt that our bodies are different from one another.  Some people can lose weight relatively easily while others struggle like hell to lose weight and by merely looking at food they seem to gain it back.  It makes perfect sense to blame our physiology on our lack of weight loss.  Blaming our behaviors is painful to acknowledge because blaming our behaviors means that “we” failed.  The problem is “us” not our bodies.  Again, I completely agree that some peoples’ physiologies make it harder for them to lose weight.  We need to acknowledge this and move on.  Because if we dwell on physiology we are dwelling on something we can’t control and squandering our energy on excuses rather than action.

So what is the bottom line, should you try to lose weight fast or slow? 

The Answer is FAST!!

Not only do individuals who lose the most weight in the first two months of a weight loss program lose more weight in months 3, 4, 5, and 6, but they keep more weight off for years to come.  Our recommendation is to lose as much weight as you can in the first 2-3 months on a diet and then try to maintain that weight loss for a number of months, likely close to a year before attempting another 2-3 month weight loss bout.  This is going to take a lot of patience but the alternative is yo-yo dieting failure.  And this isn’t because of physiological factors, this is because it is just so damn hard to keep your calories so low for so long.  The important question that you need to be able to answer is

How you transition into and out of your low calorie bouts?

What good is losing a bunch of weight and gaining it all back?  Now you’re a yo-yo dieter again.  The Science of Dieting (Todd’s 12 Steps to Healthy Eating) is developing an online course for how to transition back into “normal” dietary patterns.  It is beyond the scope of this article to try to explain it all.  But to answer one simple question out of many, should you try to lose weight fast or slow?  The answer is most definitely FAST!