Yo-Yo Dieting

Diet studies are interesting to read and have fascinating data to look at. The first thing that strikes you is how many of the study participants quit partway through the study – typically 50-80%! (See the topic ‘Staying Motivated’) The second thing that you notice is that weight loss occurs early on but nearly all of it is regained within 3 years – the end time point of most research studies. There are some follow-up studies and longer-term studies that show that by year five all of the weight has been regained plus a little extra. For those who are constantly trying diet after diet (Yo-Yo dieters) the long-term effects are a steady increase in overall body fat.

The reason behind this can be seen in the included graphs. In graph #1 we see that a typical diet (whether or not exercise is included) includes a dietary calorie restriction – the black line. Almost every diet has some kind of this unsustainable starvation included. Many people can maintain this restriction for two or three weeks, maybe a month, but we always see a huge decrease in diet adherence over the following months until calorie intake returns to where it was before the diet. Graph #2 shows what body weight (in blue) and fat mass (in green) during this same time (all of these graphs are based on data from the same original study). The change is body weight is greater than the change in fat mass meaning there is a significant loss of muscle – we will come back to this in a minute.

Now lets overlay these two graphs to make graph #3. This graph shows several things. First, fat was being lost (green line) while energy intake (black line) was less than energy intake (dark blue line) – no surprise there. Second, body weight was already starting to increase as energy intake approached energy expenditure – this is liver glycogen stores returning to normal levels as well as some protein retention by the body. Third, while energy intake (black line) returned to pre-diet levels by the 9^th month, it is taking energy expenditure (dark blue line) a lot longer to return to pre-diet levels. It will eventually sometime between year four and five, but until then ~96% of the extra energy intake is being converted to fat and stored away. By the time we get to year five body weight is higher than when we started to diet - we have more fat and still less muscle than when the diet was started (assuming little or only aerobic exercise). Well, that didn’t go as planned now did it?

So, it looks like the culprit is the calorie intake returning to pre-diet, normal levels but the energy expenditure lagging behind for a couple of years. Calorie intake returns to normal quickly as part of normal appetite function. The energy expenditure is lower as a result of the loss of the metabolically active muscle lost during the starvation portion of the diet when calorie intake levels were decreased so much (see the topic “Maintaining Muscle Mass”). Anyway, the end result is long-term fat mass gain. For someone who goes through several dieting cycles you can envision the long-term results.

So what can be done? Can diets work? (See the topics “Do Diets Work?” and “How Much Can I Lose, Which Diet is Best For Me?”)

Successful weight loss can be visualized  in graph #4. Fat and weight loss are maintained. When you look at the long-term change required to maintain that loss it comes to ~200 kcal/day lower energy intake than before as shown in graph #5. Lasting lifestyle change is key for this to work, whether dropping 200 kcal/day of something(s) from our diet or increasing physical activity 200 kcal/day or some combination (see “Weight Loss Lifestyles” topic). Change is possible and we are here to help you to plan it, see it, and be it!

Our dietCompare Calculator can show you what calorie level can best minimize muscle loss. 

Check it out at: www.myfuturefigure.com/dietCompare_Calculator.html