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New research questions a well-established explanatory model of obesity. Maskot/Getty Images
  • A popular theory asserts that carbohydrates in nutrient cause a spike in insulin, which promotes fat storage and increases ambition, leading to overeating.
  • However, contempo research suggests that this "carbohydrate-insulin model" may be an oversimplification.
  • In an article in the journal Science , researchers argue that while low carb, high fat diets tin help some people lose weight, a more than nuanced model is needed to explain how they work.
  • They write that insulin levels between meals, and the hormone's effect on multiple organs, are more important for balancing the body's energy budget.

For decades, the causes of obesity — and the nearly effective way to lose weight — accept been the subject field of fierce debate among scientists and healthcare professionals.

According to one theory, known as the "saccharide-insulin model," food and drinkable that comprise big amounts of carbohydrates cause a spike in circulating insulin levels.

The hormone drives fat cells, or "adipocytes," to store the backlog calories, which reduces the availability of these energy sources for the residual of the body.

This, in turn, increases hunger and slows metabolism, which leads to weight gain over time.

Dietitians oftentimes cite the carbohydrate-insulin model to explain the success of loftier fat, depression carbohydrate diets such as the ketogenic diet.

Dissimilar carbohydrates, dietary fatty does not cause a fasten in insulin levels immediately after a meal.

On the other side of the debate, the free energy balance model makes less of a stardom between fatty and carbohydrates.

This model focuses instead on the balance between full calorie intake through eating and drinking, and total calorie expenditure through physical activity.

According to this model, if calorie intake exceeds expenditure, the result will be weight gain over time. But if expenditure exceeds intake, the eventual upshot will be weight loss.

Writing in the journal Scientific discipline , two scientists contend that the carbohydrate-insulin model is overly simplistic.

John Speakman, from the University of Aberdeen in the United Kingdom, and Kevin Hall, of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, MD, exercise non dispute the success of high fat, low carb diets for some individuals.

They also acknowledge that insulin plays an important role in body fat regulation.

Simply they question whether the result of insulin on adipocytes after eating food loftier in carbohydrates is solely responsible for weight gain.

They write:

"[Due west]east propose that the role of insulin in obesity may be better understood past because its action on multiple organs that is driven by factors more often than not independent of saccharide intake. Reconsidering the office of insulin may better our understanding of the causes of obesity and its treatment."

They cite a 2020 study in mice that compared the effect of 29 different diets on body fat.

Of these, 16 diets maintained a abiding intake of protein while varying the relative contribution of fatty and carbohydrate to full calorie intake.

The carbohydrate-insulin model predicts that the more carbohydrates are in a diet, the college insulin levels will climb later eating.

Equally a event, according to the model, the mice should lay down more fat and increase their total calorie intake.

However, after 12 weeks — roughly equivalent to 9 years in humans — mice that ate high carb diets consumed fewer calories and had gained less fat and overall torso weight.

This was despite having higher circulating insulin levels post-obit eating.

Acknowledging that studies in mice may not reflect what happens in humans, the authors cite research in people that produced similar results.

For case, another recent written report compared the effect of two diets on people with backlog weight.

Each diet lasted for ii weeks. One comprised around 10% carbohydrate and 75% fatty, while the other consisted of approximately 75% sugar and 10% fat.

Participants were allowed to consume every bit much or as petty as they wanted.

Equally predicted by the carbohydrate-insulin model, the loftier carb diet resulted in a larger spike in insulin levels following meals.

However, participants on the high carb diet consumed fewer calories and reported that they felt but as satisfied after eating compared with those on the low carb diet.

Only the high carb diet resulted in a significant loss of body fat.

Speakman and Hall contend that insulin affects many organs effectually the body, and not just afterward mealtimes.

They write that its role in regulating trunk fat "is best understood every bit part of a dynamic network of factors controlling and mediating the effects of free energy imbalance."

For case, they say high insulin levels, combined with signals from fatty tissue, tell the brain to reduce energy intake when the amount of trunk fat rises above a critical threshold.

David Ludwig, M.D., Ph.D., professor of diet at Harvard School of Public Health in Boston, MA, a leading proponent of the carbohydrate-insulin model, questioned the enquiry cited in the article past Speakman and Hall.

He told Medical News Today that the study in mice was "strongly biased" considering the low carb diets independent large amounts of saturated fat.

"In rodents, saturated fat causes astringent inflammation and metabolic dysfunction, precluding a meaningful test of the [carbohydrate-insulin model]," he said.

He added that other studies have establish that rodents on high carb diets chop-chop develop obesity.

He as well challenged the validity of relatively brusk studies in humans, such as the 2-week report cited by Speakman and Hall, which he said do not give the body sufficient time to adapt to the change in nutrients.

His own meta-analysis suggests that longer studies consistently show higher energy expenditure on depression carb diets. Dr. Ludwig has likewise written an opinion piece as a retort to Speakman and Hall.

Several reviews of clinical trials have shown that depression carb, high fat keto diets promote weight loss.

Prof. Naveed Satar from the Institute of Cardiovascular and Medical Science at the University of Glasgow in the U.K. told Medical News Today that depression carb diets can assistance people lose weight.

He believes the diets owe their success to lower total calorie intake as a result of reduced ambition, but not from how some experts envisioned the workings of the carbohydrate-insulin model.

"People who go on low carb diets tend to eat less as they increment poly peptide intake, which tends to suppress ambition a piffling," he explained.

He added that his own enquiry suggests that the excess calorie intake of individuals with excess weight tends to come from fat rather than carbohydrate.

This suggests that, forth with reduced calorie intake, reduced fat intake should remain an of import component of weight-loss diets.