Is yo-yo dieting bad for you? Here’s what recent research has shown

The only thing harder than losing weight is keeping it off. Many people who lose weight find themselves stuck in the cycle of “yo-yo dieting” – losing weight and gaining it all (and sometimes more) again.

Research on yo-yo dieting has long shown that it can be harmful to your health. But a new paper has now suggested that yo-yo dieting may not be as healthy as we’ve been led to believe.

This latest paper, published in BMC Medicine, presents the findings of two separate weight loss trials that were conducted five years apart.

The first session (session 1) looked at 278 overweight or obese participants. Participants were randomized to follow either a low-fat or low-carb Mediterranean diet – either with or without exercise. All participants lost a comparable amount of weight at the end of the 18-month trial. But those who included exercise achieved the greatest reduction in visceral fat (a dangerous type of fat stored around the organs).

The second experiment (experiment 2) was conducted five years later. Similar to trial 1, 294 participants followed a Mediterranean-style diet for 18 months. But this time, one group ate a diet very high in foods rich in polyphenols (natural plant compounds associated with health benefits such as a lower risk of chronic disease). The second group ate a normal Mediterranean diet, while the third group followed normal healthy diet guidelines.

While both Mediterrananean diet groups lost weight and saw improvements in their overall health, the polyphenol group lost more visceral fat.

A unique aspect of trial 2 was the inclusion of around 80 participants from trial 1. Some of these participants weighed more than they did at the start of the first trial. Weight recidivism like this is common after weight loss. This is due to various biological and physiological functions that reduce metabolism and increase hunger, causing people to regain weight and store fat.

The author compared people who rejoined the research project against their health and weight status at the beginning of trial 1. They assessed body weight and other aspects of health – including body fat and blood sugar levels. Although the re-joiners weighed around the same (if not more) than they did at the start of trial 1, they had lower levels of abdominal fat and visceral fat five years later.

Their metabolic health was also better than at the start of the first trial, based on blood lipid (fat) levels, cardiovascular health and blood sugar control.

On the surface, this appears to be good news – suggesting the participants retained some of the health benefits of the weight they lost the first time around, despite regaining weight.

However, the results show that the very adaptations that help re-joiners stay healthy despite losing weight can potentially have consequences later. Understanding why this is the case requires understanding how the body responds to a calorie deficit.

Lose weight and body fat

Our fat stores (known as adipose tissue) serve as our main energy (calorie) buffer when there is no food to provide that fuel. These stores are sacrificed to cover the lack of energy, causing fat cells to shrink. Visceral fat is the first to go, followed by more useful fat cell stores.

But when people stop dieting, the body puts priority on regaining lost fat. Indeed, our body replenishes fat store much faster than it does not store muscle or protein. More importantly, in response to this reduction, the body compensates by making more fat cells. This is done to help the crew perform better the next time there is a fuel crisis.

So dieting literally makes you fatter in the long run. But fortunately, this is most likely to be healthier subcutaneous fat (in the hips, thighs, buttocks and torso) rather than around the organs as harmful visceral fat.

So even if you will carry excess weight, you will experience fewer metabolic problems caused by unwanted visceral fat – such as insulin resistance and high cholesterol, which elevate your risk of cardiovascular disease and diabetes.

But with a higher capacity to store fat comes the risk of overshooting your original weight. This may also have implications for yo-yo dieting.

Weight loss cycle

In the paper, the re-joiners who took part in trial 2 did not manage to lose weight again. But, on average, they lose a little less than the first trial. That said, when all the participants from trial 2 were followed up five years later, re-joiners from trial 1 have regained less, too. It also holds more weight loss health benefits.

Looking at all the weight loss journeys, it appears that those who regained weight and then took part in trial 2 were in a comparable place at the end of ten years to those who had just done trial 1.

But there are some caveats to the trial’s findings.

First, the paper measures body fat. It does not provide information about lean tissue (such as muscle). This is important, as when we lose weight we lose both fat and muscle. Because of the importance of muscle to a healthy metabolism, a lack of muscle can lead to greater weight gain.

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Read more: weight loss: why you don’t just lose fat when you’re on a diet

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It is also not clear why regaining weight changes the properties of muscle tissue. There are two key types of muscle fibers. Type 1 is smaller and more efficient in burning fat. Type 2 is bigger, faster and stronger – essential for explosive training.

If the loss of all muscle causes muscle fibers to change from type 1 to type 2, this can increase the risk of health problems – including sarcopenic obesity and early onset of age-related health problems associated with muscle loss.

Overall, the paper shows that weight loss is still beneficial for your health — even if it takes some effort to reach your goal weight. But to avoid the possibility of gaining weight a second time, it is important to establish a good diet and long-term sustainable lifestyle changes.