- A new study finds that the success of weight-loss methods depends on your starting body weight.
- Of the groups studied, people with obesity benefited the most from all weight-loss methods, gaining the least weight afterward and lowering their risk of developing type 2 diabetes.
- However, people who are already lean when they lose weight may weigh more than they did when they started.
A new observational study from researchers at the Harvard TH Chan School of Public Health in Boston explores associations between weight-loss methods and regaining weight, as well as the subsequent risk of developing type 2 diabetes (T2D).
The study found that outcomes depended on a person’s weight at the outset of weight loss.
People were categorized according to Body Mass Index (BMI) as obese — with a BMI equal to or greater than 30 — overweight (a BMI of 25–30), or lean (a BMI of less than 25.) Within these categories, they compared people who intentionally used weight-loss strategies to lose 4.5kg with those who did not attempt to lose weight.
The study included assessments of the following weight-loss strategies:
- low calorie diet
- exercise and low calorie diet
- commercial weight-loss program
Researchers also measured the outcomes for people using a combination of two or more methods, including fasting, commercial weight-loss programs, or pills — abbreviated as “FCP.”
All the studied weight-loss methods, except the pill and FCP, were effective for people with a BMI ≥30.
The study also found that among people with obesity, those who lost 4.5kg intentionally, regardless of weight-loss strategy, gained less weight over four years and had a lower risk for developing type 2 diabetes over 24 years than those who did not attempt weight loss.
For people with a 25–30 BMI, associations of weight-loss strategies and eventually regained weight and diabetes risk were more complex.
Except for those who used exercise, people with a BMI <25 who deliberately lost 4.5 kg of weight regained more weight and had a higher risk of developing type 2 diabetes than those with a BMI <25 who did not attempt weight loss.
Dr. Mir Ali, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, California, not involved in the study, told Medical News Today:
“These findings are surprising because it would seem that weight loss would be beneficial for everyone. Based on this study, lean individuals seem to have a different biological makeup.”
The study appears in the journal PLOS Medicine.
After adjusting for variables, compared to those who did not attempt weight loss, the weight loss for the ≥30 BMI group after four years was 4.2% with exercise, 2.7% with exercise and diet, and 1% with a low calorie diet alone. The weight loss for fasting was 2.1% and 1.9% for commercial weight loss plans. The results for pills and the combined FCP approach were not statistically significant.
Almost all weight-loss strategies lowered the risk of type 2 diabetes in people with obesity compared to those who did not attempt weight loss.
The group who used exercise had a 21% relative risk reduction, as did those who combined exercise with a low calorie diet. The relative risk reduction for diet alone was 14%, while for the commercial weight loss program group, it was 13%.
“Obesity causes significant hormonal and metabolic effects that are detrimental to most individuals. By losing weight, obese individuals are reversing these effects,” said Dr. Ali. “Obesity causes increased fatty acids and inflammation, which ultimately leads to insulin resistance, thereby making the individual more susceptible to diabetes.”
For this group, weight loss after four years compared to those who did not attempt weight loss was 2.5% for exercise alone, 1.2% for exercise and diet, and 0.9% for a low calorie diet alone.
The results for fasting, commercial weight-loss programs, and the pill were not statistically significant.
In the same group, compared to those who did not attempt weight loss, the risk of type 2 diabetes was increased by 42% by use of the pill and 16% by use of commercial weight loss programs.
The results for exercise, fasting, diet, and diet plus exercise were not statistically significant.
The study found that deliberately losing weight may not be a healthy strategy for people with a BMI of less than 25.
Dr. Catherine Womack, not involved in the study, is a researcher in public health ethics, specializing in eating and activity health promotion and weight discrimination at Bridgewater State University, Massachusettes. Dr. Womack explained to Medical News Today:
“Living in a world that judges everything we eat, approves of dieting under any circumstances, and compliments weight loss even when caused by illness makes weight loss a universal imperative.
Studies looking at weight talk during annual medical checkups of normal weight people (BMI<25), note that commonly, providers will say, ‘well, you’ve gained four pounds,’ as if this is a problem for a non-overweight person.”
“Any weight gain at all is seen and reinforced as implicitly negative or harmful or a potential threat to health, which [it is] not. Weight fluctuates, and also, over the life course, most people gain weight,” Dr. Womack explained.
The study found that after four years, this group almost universally gained more weight than those who did not attempt dieting. Only with exercise alone was this not the case, where they gained just 0.4% less than non-dieters. With dieting alone and fasting, they gained 1% more; with diet plus exercise, they gained 1.1% more; with the pill they gained 2% more; with commercial weight-loss programs, it was 2.9% more, and with FCP, they gained 3.7% more.
The relative risk for developing type 2 diabetes in this group increased with all weight-loss strategies except exercise, which was not a statistically significant result. Pills and FCP were most damaging, increasing the relative risk of type 2 diabetes by 54% compared to those who did not attempt weight loss.
“Lean individuals have a different hormonal and metabolic baseline than overweight people,” said Dr. Ali. “This study showed intentional weight loss affected them differently. There is clearly an underlying biologic difference that needs to be understood further.”
“Some recent studies on FFM — ‘fat-free mass,’ [which is] our total body weight minus the weight of our body fat — suggest that [FFM] is a better marker of longevity and mortality risk than BMI, especially in older populations,” Dr. Womack noted.
“This is yet another intriguing result that suggests that body fat itself is a less important marker of overall health than other body features,” she added.
Dr. Womack said the type 2 diabetes risk reduction “makes sense” since exercise-induced weight loss produces more fat loss without as much FFM loss in general, and especially among heavier people.
She said looking at FFM may also explain the inverse results of the BMI<25 groups.
“Weight loss in BMI<25 groups results in loss of more FFM and loss of less body fat. Also, the virtually inevitable weight gain for that group tends to result in more fat gain and less FFM gain. This isn’t true for the BMI≥30 group. The researchers pointed this out as a possible reason,” she explained.
“It’s possible that some of the weight loss in the BMI<25 group is the result of disordered eating,” Dr. Womack expressed her concern, although she suspects the studies upon which this research was based likely took this into account.
“There’s evidence that people with a history of eating disorders have an increased risk of T2D,” she added.
“It seems clear that clinicians can use [the study’s] results to reinforce a shift towards encouraging and educating patients about physical activity vs. recommending weight loss through diet strategies,” said Dr. Womack.
“The main takeaway is that weight loss is beneficial for those who are overweight. Lean individuals did not experience the same or more benefit,” said Dr. Ali.
Speaking about the difficulties of maintaining weight loss, he said, “The most common mistake I see is individuals not making sustainable lifestyle changes. Most diets will work, but the weight comes back when a person stops the diet.”
“The key is making dietary and exercise changes that can be maintained long-term,” Dr. Ali added.