Is just 4.5 kg of weight loss really going to help stop type 2 diabetes?

A new study has found that losing just 4.5 kg of weight could be the difference between getting type 2 diabetes and not.

That’s the headline on some of the publicity surrounding the research, except like all these studies, it’s significantly more complicated than that. So, let’s talk about it.

The study looked at around 100,000 nurses and other health professionals from a few different US cohort studies that started in the late 1980s.

The team looked at up to 10 years of weight changes and tracked the participants for 24 years to see if they developed type 2 diabetes.

They also looked at the way that those who lost more than 4.5 kg, dieted. They split them into seven categories – low-calorie diet; exercise; low-calorie diet plus exercise; fasting; commercial weight loss program; diet pills; and a combination of fasting, commercial and diet pills.

When the team looked at the original results, they found something surprising: In the overall population, those who lost more than 4.5 kilograms had a higher risk of being diagnosed with type 2 diabetes than those that didn’t diet or try and lose weight.

This was particularly striking for those that lost the weight due to limiting calories, diet pills, fasting, or weight loss programs.

The researchers then split the data into BMI categories – those who were ‘normal’ weight or underweight, those who were overweight and those who were obese.

Read more: Why some people find it easier to lose weight

The findings of a higher risk of type 2 diabetes after trying to lose weight broadly held in both the ‘underweight’ and ‘normal’ as well as the ‘overweight’ categories.

“We were a bit surprised when we first saw the positive associations of weight loss attempts with faster weight gain and higher type 2 diabetes risk among lean individuals,” says Qi Sun, a nutrition researcher at the TH Chan Harvard School of Public Health.

As you can see in this figure below, the risk of type 2 diabetes only reduced a little – significantly less than the increased risk of type 2 diabetes if you lost over 4.5 kilograms while at a normal BMI.

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Hazard ratios for association between weight loss strategies and the incidence of type 2 diabetes by baseline BMI. Credit: Si et al., PLOS Medicine, 2022

As noted in the paper, the vast majority of people try and diet at some point or another – in 2013 to 2016 almost half of US adults reported trying to lose weight.

But almost everyone either doesn’t succeed or puts all the weight back on, normally within a few months.

This study backs that up. After 10 years, those who tried to lose weight (known as the weight loss strategies group) gained more weight than those that hadn’t.

“Participants who lost 4.5+ kg were likely to gain more weight and have higher risk of type 2 diabetes than those who did not attempt to lose weight,” the team writes in their paper.

“By 10 years of follow-up, all weight loss strategy groups were associated with more weight gain than the reference group (ranging from 1.7% for exercise to 6.6% for fasting, commercial weight loss program and pills).”

It’s important to note here that exercise and eating well is not bad for you. Exercise has been shown time and time again to help us live longer, and eating more fruits and vegetables and less processed food is better for us.

However, this study is a good reminder that just losing weight – particularly in ways like weight loss pills, calorie restriction and weight loss programs are not a silver bullet for keeping us healthy.

In fact, depending on who you are, it seems it might make it worse.

The conclusion from the study is worth reading in full:

In conclusion, in individuals with obesity, losing 4.5+ kg of body weight intentionally was associated with less weight gain and lower T2D risk, regardless of the methods used to achieve the weight loss. However, for individuals who were lean, losing 4.5+ kg was not associated with these health benefits. Of all WLSs, exercise was optimal for long-term weight control and T2D prevention. Our data support current guidelines for body weight management, such as that issued by the Obesity Society, which recommend a weight loss of 5% to 10% of baseline weight for individuals who are overweight or obese and exercise of 200 to 300 minutes per week to maintain the weight loss.

The research has been published in PLOS Medicine.

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