Is dieting making us fatter?

Let’s start our exploration with some stats around fat loss. How many people do you successfully believe reduced their body weight over the long term? Let’s say we define success as a 10% reduction in body weight that lasts one to three years. What do you think is a reasonable success rate? Well, here’s the data we have now. Less than 20% of the people who reduce their weight by that level, keep it off after one year. After two years, it’s about 15%. Three years, and it’s around 5%. That means if your clients are average people and you take 10% of the total body weight off of 20 of them, only one will likely keep that weight off.

It sounds pretty depressing, right? Well, it gets worse

Of the people who regain the weight they lose, between one third and two thirds of those people will end up heavier than they started. That means they don’t just put on the 10% they lost. They put back on additional weight above that. Effectively, they take one step forward and two steps back.

Pretty scary, huh? Just wait.

There’s a growing body of evidence that not only do a large proportion of people put on more weight than they started with, but it also appears that the amount of additional weight they put on is proportional to the number of times they have attempted to diet in the past. This means that every time they tried to diet and fail to maintain weight loss, they gain more weight than before. No wonder we have an obesity epidemic, even though six out of every seven obese people will lose a significant portion of their weight in their life.

Now let’s take a look at some interesting evidence. This graph is based on research from the TV show, The Biggest Loser. Now, if you’re not familiar with this show, the premise is simple. A group of obese individuals are subjected to the most aggressive and unsustainable diet and exercise regimes imaginable. They are basically starved and trained like crazy and amazingly, they lose tons of weight. In fact, the participants in this study saw on average a weight reduction of nearly 40%, and we’re talking about people who were about 150 kilos starting. Their resting metabolic rate, or RMR, similar to BMR, was measured, and from that measurement, estimation formulas were calibrated. Over the course of the show, participants lost a significant amount of weight. Not too shocking, given the massive energy deficits (Fothergill et al., 2016).

While RMR was predicted to have gone down based on changes in overall body mass, it actually went down more than expected. That’s not weird because we have evidence that shows that metabolic adaptation is disproportionate to the amount of weight that was lost during a diet (Doucet et al., 2001)(Michael Rosenbaum et al., 2008)(M. Rosenbaum & Leibel, 2010). What is interesting is the study continued for six years after the conclusion of the show, and what happened after defies logic. On average, participants regained nearly all the weight they lost. But that’s not the most interesting bit. We would have expected their RMR to increase given the substantial increases in body mass, but for these participants , it actually continued to stay down even as they were gaining weight (Fothergill et al., 2016).

This is a shocking outcome and one that really makes you question the methods that were used to achieve the results. In fact, the metabolic adaptation that was calculated after the six year period was 500 calories, meaning their daily energy expenditure was 500 calories lower than was predicted based on their body mass.

Now, here’s some more interesting research data. Researchers used a rat model to understand how rebound weight gain works in yoyo dieting. Rats were dieted down through caloric restriction then allowed to regain the weight back to baseline and they measured how long it took to lose the initial weight and regain it. Not shockingly, the rats were able to regain the weight much faster than they lost it. Actually two times as fast (Brownell et al., 1986).

The researchers let them rebound to their original weight and then dieted them down again. Now they were on the same calorie deficit that they were on the first time, but this time it took them twice as long for them to lose the weight as the first time they lost it. And when they reached the weight loss goal and they let them eat whatever they want, the rats put the weight back on three times as fast as their initial weight loss rate. In each dieting cycle, the rats lost and regained the same amount of weight, but each time it took them longer to lose it and less time to regain it.

Now you might be thinking, “well, that’s great for rats, but I’m a human. What does that have to do with me? ” Well, that’s a fair criticism and it’s good to think that way when trying to make decisions based on data like these, but remember from our earlier lesson on research in nutrition, that doing human studies of this nature are really difficult. You would have to have humans in a metabolic ward for a really long period of time and in high numbers, and that would be expensive and costs millions of dollars, and I’m not aware of any research institute that actually has the capability of doing something like that.

So I think it’s important to remember that if you want really controlled research in humans, it’s going to be a low subject number and for a short period of time. If you want a high subject number in humans, it’s probably going to be more loosely controlled, and if you want it a high subject number over a long period of time, it’s going to be very loosely controlled. If you want a high subject number with a lot of control, then it’s going to have to be likely in rodents.

So I don’t ever want to make decisions just based on one piece of data, but this does seem to fit some of the things I’ve observed with clients over the years. That said, there is some human data that points in the same direction as the yoyo diet study in rats. There’s data from twin studies that show that twins who attempted to diet at more during the lifetime had more fat gain (Pietiläinen et al., 2012). So this is controlling for a little bit of the genetic variability because you could claim that it’s not that dieting makes people fat it’s that fat people are more likely to diet. Likewise, studies of athlete populations have shown that those who had to diet to make weight classes end up gaining more weight after their career is over versus those who didn’t have to diet to make a weight class.

While there aren’t a ton of studies, what has been done and collected around body fat overshooting or rebounding, was well documented in a paper by Dulloo et al. This paper was entitled How Dieting Makes Some Fatter From the Perspective of Human Body Composition Autoregulation. They reviewed seven human studies and the impact of caloric restriction on subsequent weight regain after the subjects finish the diet (Dulloo et al., 2012).

Now after the diet was over, the humans were allowed to eat what’s called ad libitum, meaning as much as they wanted. The findings were pretty concerning. Two studies by Benedict one, looking at total fasting and semi-starvation, looked at outcomes after this total fast or semi-starvation was done and saw that even these short periods of fasting, they saw body fat overshooting of between 2.7 to 3.1 kilograms, meaning they put on in addition to what their weight originally was, 2.7 to 3.1 kilograms of fat more than that.

There was an experiment performed by Fleisch, which was the Swiss food rationing experiment where the Swiss Federal Commission for Wartime Feeding, again during World War II, started rationing food because they had limited resources. So Fleisch studied the 700 subjects and their subsequent health outcomes spanning different age groups, socioeconomic status and geographies. After five years of food rationing, weight regain was monitored in the subjects, and on average they regained 6.5 kilograms more fat than they had before food rationing.

Then we have the famous Minnesota Starvation Experiment performed by Ancel Keys. Now they took conscientious objectors to World War II and put them on about 800 calories for about six months. At the end of the six months, subjects lost about 25% of their body weight on average. But once they were allowed to refeed on an ad libitum diet, they went back up to the original fat mass and then overshot that by 3.3 kilos of fat. Now, an interesting side note about the Minnesota Starvation Experiment (Keys et al., 1950). I believe that the original number of people in the study was 15. It was down to 12 by the end because one person mutilated themselves to get out of the experiment. I believe he cut off his thumb. And then two more literally assaulted the kitchen in an attempt to get more food, and of the people who remained, I believe four went on to become professional chefs or work in the food industry. Those of you who have dieted before and became preoccupied with food, this might make more sense.

More contemporary studies of populations in the US Army Ranger School had similar results. Both Nindl et al, and Friedl et al studied groups subjected to multiple weeks of stressful Army training, which included caloric restriction of about 1800 to 2000 calories a day (Nindl et al., 2007)(Friedl et al., 2000). But what’s interesting to note is they’re doing exercise about 12 to 14 hours per day, and most of that being with weight packs on their back. In the case of Nindl, the subjects regained and overshot their original weight by five kilos with a significant portion coming from fat (Nindl et al., 2007). Friedl found a 2.4 kilogram overshoot with about 40% occurring in body fat (Friedl et al., 2000).

So what we can conclude from Dulloo’s review of these human studies is that it’s pretty clear that if you lose a significant amount of weight, then allow uncontrolled ad libitum consumption to follow, your body is going to seek to regain all the weight you lost and then some. Second, we can further conclude that the extra weight gained isn’t likely to be of the lean body mass variety.

Perhaps the most important conclusion we can draw from Dulloo’s work is that when it comes to weight loss, it’s not enough to just lose a bunch of weight. If the point is to improve health, wellbeing, lifestyle, and appearance, what’s the point of losing a ton of weight only to gain back a ton and a half?