Published by Jack Pryor and Stephanie Simonds
Department of Physiology, Monash Biomedical Discovery Institute, Monash University, Australia
These findings are described in the article entitled Repeated weight cycling in obese mice causes increased appetite and glucose intolerance, recently published in the journal Physiology & Behavior (Physiology & Behavior 194 (2018) 184-190). This work was conducted by Stephanie E. Simonds, Jack T. Pryor, and Michael A. Cowley from Monash University.
A new year; a new you: If this year new actually means thinner then perhaps you’ve made this resolution before, and maybe you’ve failed to stick to it. Hence you’re back at it.
The Internet abounds with myriad diets and exercise regimes that claim to have the fat-burning solutions you seek. Hence your local gym feels like Shibuya in January yet come March it’s empty again, frequented only by those whose masochism, narcissism and/or fear of the grave are sufficient to sustain year-round discipline.
Also, we’re fickle: We watch our dietary intake for a few weeks and actually enjoy our workouts to start with; “I’m actually going to do it this time”. Then after a few weeks we see the hint of an abdominal or jawline, at which point we feel as though we’ve won the weight loss challenge so we celebrate with three months of Mars bars and lager. Before we know it we’re back at square one doing it all over again and hating ourselves for it.
Whatever the reasoning for this pattern of yoyo dieting it’s becoming increasingly apparent that allowing our weight to fluctuate is bad for our metabolic health in the long term.
In order to explore how successive bouts of high calorie and low-calorie feeding affects metabolic health, our team based at Monash University sought to replicate this sort of yoyo dieter in a mouse model. We recently published this work in the journal Physiology and Behavior.
In this study, we compared mice that were continuously fed a high-fat diet (HFD) for 8 weeks with mice subjected to a “yoyo diet” for 8 weeks. Of this latter group, mice received two cycles of 2 weeks of a high-fat diet, followed by 2 weeks of a low-fat diet. We did not investigate the effects of exercise in this study.
In brief, the results are as follows:
Yoyo diet mice ended up just as obese as mice fed an exclusively high-calorie diet.
- Yoyo diet mice had worse glucose tolerance than mice fed an exclusively high-calorie diet. (Glucose tolerance is a measure of the body’s ability to absorb glucose from the blood into tissues following a meal. Impaired glucose tolerance is a risk factor for type-2 diabetes.)
- Of yoyo diet-cycled mice, with each reintroduction of high-calorie food, mice ate more of it. They became increasingly driven to eat high-calorie food with each successive cycle. Mice also regained weight at a quicker rate each time.
- After 4 diet cycles, yoyo mice metabolic rate was lower than mice only fed high-calorie food. Here, it would seem that mouse physiology adapts to a “starvation state” and functions to conserve more energy thereafter. This effect is exacerbated with each subsequent cycle. This phenomenon seems somewhat similar to anecdotal accounts from yoyo dieters, who find each period of dieting less successful than the last. This is also a phenomenon experienced by athletes such as boxers who are required to “cut weight” before competition.
- After four diet cycles, yoyo mice were less physically active than mice only fed a high-calorie diet. Yoyo diet cycling appears to make them lazier.
In conclusion, yoyo dieting doesn’t work in the long run. It impairs glucose tolerance, elevates appetite for high-calorie foods, diminishes metabolic rate, and reduces activity levels.
We are continuing this work to investigate sex differences and to take into account the effects of exercise on yoyo dieting. In doing so, we will hopefully shed more light on the underlying physiological processes preventing effective and sustainable weight loss in obese individuals and professional athletes alike.
The extent to which these results can be generalized to humans remains unclear, only time — and more experiments — will tell. For the time being, the take-home message from research like this is that what we need to find a sustainable diet and a form of exercise that we actually enjoy as an individual. Only then can will we be able to kid ourselves into enjoying the whole affair and use it as a coping mechanism as opposed to the first thing to go out the window when life gets tricky.
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