New research challenges what we know about yo-yo dieting

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) back again.

Research on yo-yo dieting has long indicated it can be harmful for your health. But a recent paper has now suggested yo-yo dieting might not be as unhealthy as we’ve been led to believe.

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

The first trial (trial 1) looked at 278 participants who were overweight or obese. Participants were randomised 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 incorporated exercise achieved the biggest decrease in visceral fat (a dangerous type of fat that is stored around the organs).

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

While both Mediterrnanean 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 that it included around 80 participants from trial 1. Some of these participants weighed more than they did at the start of the first trial. Such weight recidivism is common following 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 authors compared the people who rejoined the research project against their health and weight status at the start of trial 1. They assessed body weight and other aspects of health – including body fat and blood sugar levels. Despite the re-joiners weighing 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 it was at the start of the first trial, based their blood lipid (fat) levels, cardiovascular health and blood sugar control.

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

Yet, the results suggest that the very adaptations which helped the re-joiners stay healthy despite regaining weight could potentially have repercussions later. To understand why this is the case requires a grasp of how the body responds to a calorie deficit.

Weight loss and body fat

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

But when people stop dieting, the body puts priority on regaining lost fat. Indeed, our body replenishes fat stores far more quickly than it does muscle or protein stores. More importantly, in response to this shrinkage, the body compensates by making more fat cells. It does this to help the body better cope the next time there’s a fuel crisis.

So dieting literally makes you fatter in the long run. But thankfully, this will most likely be healthier subcutaneous fat (in the hips, thighs, buttocks and torso) instead of around the organs as harmful visceral fat.

So even though you’ll be carrying excess weight, you’ll experience fewer of the metabolic issues caused by unwanted visceral fat – such as insulin resistance and high cholesterol, which elevate your risk of cardiovascular disease and diabetes.

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

The weight loss cycle

In the paper, the re-joiners who took part in trial 2 did manage to lose weight again. But, on average, they lost slightly less than the trial’s first-timers. That said, when all of the participants from trial 2 were followed up five years later, the re-joiners from trial 1 had regained less, too. They had also retained more of the health benefits of losing weight.

Taking stock of the whole weight-loss journey, it appears that those who regained weight and then joined trial 2 are at a comparable place at the end of ten years to those who just did trial 1.

But there are a few caveats to the trial’s findings.

First, the paper only examined body fat. It didn’t provide any information on lean tissue (such as muscle). This is important, as when we lose weight we lose both fat and muscle. Given muscle’s importance for a healthy metabolism, a lack of muscle could result in even greater weight gain.

It’s also not clear whether regaining weight changes the nature of muscle tissue. There are two key types of muscle fibre. Type 1 is smaller and more efficient at burning fat. Type 2 is larger, faster and more powerful – important for explosive exercise.

If an overall loss of muscle results in muscle fibres changing from type 1 to type 2, this could increase risk of health problems – including sarcopenic obesity and earlier onset of age-related health issues associated with muscle loss.

Overall, the paper shows us that weight loss is still beneficial for your health – even if it requires a few attempts to get to your goal weight. But to avoid potentially gaining more weight the second time around, it’s key to establish good diet and lifestyle changes that are sustainable long-term.