Don’t go on a diet to lose weight if you’re not obese…, says the Harvard study

A major study suggests that going on a dramatic diet to lose weight when you’re not obese could harm your health years later.

Already lean people who lost 10 pounds (4.5 kg) had a higher risk of developing type 2 diabetes a decade later compared to their peers who didn’t go on an extreme diet.

They were also more likely to pack on pounds lower down, according to research from Harvard University.

The scientists said their results were “surprising”.

But they believed that thin people who experienced dramatic weight loss had higher levels of hunger hormones, which made them more likely to crave junk food.

Many thin people try to lose fat in hopes of achieving Instagram-style washboard abs or a more toned physique.

But the Harvard team now warns that dramatic weight loss diets should only be used by those who “medically need them”.

The results also showed that thin people who lost weight by following a fad diet or commercial weight loss program were more likely to gain weight later in life.

About 40 percent of American adults are overweight, but a previous study found that half of women and 20 percent of thin men believe they fall into that category as well.

The chart above shows weight change after ten years in people who were considered thin (blue bars) or obese (red bars) at the start of the study and who experienced extreme weight loss of up to 9.9 pounds (4.5 kg). It is divided into the method used to lose weight (the left-hand column gives labels) and the amount of weight lost or regained over ten years compared to people in the same group who did not experience extreme weight loss. All those in the thin group who tried extreme weight loss regained more weight than their peers, up to 17 pounds (7.7 kg) more, the study says. But in the obese group, four of the groups managed to maintain more weight ten years later, up to four pounds (1.2 kg) less.

Many skinny people try to cut their weight with the goal of achieving washboard abs and toned “Instagram-ready” bodies. But scientists warned that this was bad for their health

In what is believed to be the first study of its kind, experts analyzed data from 200,000 healthy Americans collected between 1988 and 2017.

Nine out of ten participants were women.

They were divided by body mass index (BMI) into those who were thin, in the healthy or underweight range, overweight or obese.


Body mass index (BMI) is a measure of body fat based on your weight in relation to your height.

Standard formula:

  • BMI = (weight in pounds / (height in inches x height in inches)) x 703

Metric formula:

  • BMI = (weight in kilograms / (height in meters x height in meters))


  • Under 18.5 years: low weight
  • 18.5 – 24.9: healthy
  • 25 – 29.9: overweight
  • 30 – 39.9: obese
  • 40+: Morbidly obese

Each was then divided into two groups: those who lost 9.9 pounds (lbs) (or 4.5 kilograms, kg) over a four-year period and those who did not.

Weight Watchers were also asked how they lost weight and were divided into seven groups: a low-calorie diet; exercise; low calorie diet and exercise; fasting; commercial weight loss program; diet pills and a combination of fasting, commercial and diet pills.

The scientists then looked at the participants’ medical records for another 10 years, on average.

Among lean people, those who followed the extreme diet gained 4.4 to 17 pounds more (2 to 7.7 kg) than their peers.

But among obese people, those who did four of the programs: low-calorie diet, exercise, low-calorie diet, and exercise and fasting lost an additional 3.5 to 1.3 pounds (1.2 to 0, 5 kg) than their peers.

The scientists also looked at the participants’ diabetes risk.

Thin people who experienced dramatic weight loss were up to 54% more likely to develop type 2 diabetes than their peers.

But obese adults who followed a strict weight loss program at some point in their lives were less likely to develop diabetes than their peers.

Dr Qi Sun, an epidemiologist at Harvard who led the study, said: “We were a bit surprised when we first saw the positive associations of weight loss attempts with faster weight gain and greater risk of type 2 diabetes among thin individuals.

“However, we now know that these observations are supported by biology that unfortunately leads to adverse health outcomes when thin individuals intentionally attempt to lose weight.

“The good news is that people with obesity will clearly benefit from losing a few pounds, and the health benefits last even when the weight loss is temporary.”

He said the weight loss likely caused biological changes in thin people that put them at greater risk of piling on the pounds later.

It can increase levels of ghrelin, the hunger hormone, making someone hungry more often.

This can also make people more likely to reach for salty or sugary foods because it activates the region of the brain associated with rewards.

Similarly, the researchers cautioned that more fat cells, which release ghrelin, could accumulate in lean people to increase levels of the hormone.

At the same time, rapid weight loss, however, leads to lower levels of anorexigenic hormones, such as leptin, which help suppress hunger.

Studies also suggest that being very thin makes people move less as a way to conserve energy, making it harder to burn calories.

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