The science behind yoyo diets

Diets, in popular culture, are seen as an effective way to lose weight. However, many know of, or have even experienced the adverse effects of dieting and its yo-yo nature; so why does this happen?

The unfortunate yo-yo effect that dieting very often brings forth is due both metabolic and psychological factors, and these happen to interplay on occasion.

When you begin to intake less food you receive less energy for everyday use and so your body begins to rely more on your energy stores of fat and protein, and this is why you begin to lose weight.

This initially seems positive, but actually has a large bearing on the yo-yo nature of dieting; the problem lies not in that dieting burns fat, but in that dieting metabolises muscle mass for energy.

Muscle plays a pivotal role in what is termed your basal metabolic rate (BMR) as even when your muscle is doing very little, it needs energy to stay alive, and due to the relatively large mass of muscle compared to other energy consuming tissues in your body, it actually uses a lot of energy each day.

So as you diet and lose muscle mass, you are gradually losing your capacity to burn energy whilst doing absolutely nothing, meaning in effect that you have to work harder to lose energy and therefore weight. This fall in BMR is one of the main reasons you may experience a plateau whilst dieting.

Where diets begin to fail is when the inherent difficulty of withholding food from yourself, atop the disappointment of reaching a weight loss plateau leads to a slight increase in your food intake. This for many possible reasons including a feeling that the diet is no longer working for you or as comfort eating.

This is where the upward stretch of the yo-yo begins and unfortunately it is a fast return, all thanks to the metabolic effects of dieting.

Unfortunately, seeing as you lose muscle mass whilst dieting you now have a lower capacity to expend energy by doing relatively little, so the energy you intake is much more likely to get stored as fat (and unfortunately not as muscle seeing as that requires initiation through chemical messengers brought about by exercise).

To make things slightly easier to understand I will explain it numerically with 3 things, your food intake, basal metabolic rate and energy expenditure (energy lost through normal daily activities), these numbers are entirely fabricated for ease of understanding:

  • Pre diet: 700[Intake] – 500[Expenditure] – 200[BMR] = 0 (Energy balance. No weight lost or gained)
  • During diet stage 1: 600 – 500 – 200 = -100 (Weight loss due to less food intake)
  • During diet stage 2: 600 – 500 – 100 (BMR resets due to lower food intake. No gain or loss of weight, plateau reached)
  • Post diet: 700 – 500 – 100 = 100 (Diet ceased. Net gain in weight due to increased food intake and lower BMR)

Thankfully there is a way to avoid this reduction in BMR, a way to lose weight whilst maintaining your muscle mass, through regular exercise. Who’d have thought?

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