Although the keto diet, which requires people to get 70% of their calories from fat, has gained popularity in recent years, the scientific community really doesn’t know the best way to balance lipids and carbs, a group of doctors writing in the journal Science conclude.
Research into macronutrition is underfunded and underdeveloped, they say, and despite the fact that diet is tied to obesity, diabetes, heart disease, and even cancer, the benefits of high-fat or high-carbohydrate diets are not well understood.
“Currently, the United States invests a fraction of a cent on nutrition research for each dollar spent on treatment of diet-related chronic disease,” writes the group, led by David Ludwig of Boston’s Children’s Hospital in the US.
They outline several “current controversies” over the health risks and benefits of different carbohydrate-to-fat proportions of diets, including the most basic unknown: Does it matter to your waistline?
“Do diets with various carbohydrate-to-fat proportions affect body composition (ratio of fat to lean tissue) independently of energy intake?” they ask. “Do they affect energy expenditure independently of body weight?”
Other controversies in the field include what types of fat people should, or shouldn’t, eat, what the long-term effects of different diets might be, and what individual, genetic, and behavioural factors interact with different food regimes.
In their review, the doctors give a brief overview of how fat became vilified in the US in the 1970s and continued to be contra-indicated even as Americans became more and more obese.
Today, though, fat is making a comeback, starring in the keto diet fad. This regime requires getting most calories from fat and restricting carbohydrates in order to prompt nutritional ketosis, the process by which the body starts burning fat directly for fuel.
The metabolic state has a range of benefits, including weight loss, according to some studies. Others, however, have identified significant dangers.
There are arguments to be made – as the review outlines – for high-fat, low-carb diets as well as for high-carb, low-fat diets, underscoring the need for more research.
The review also looks at “dietary fat quality” as a health factor. The molecular structure of fatty acids can present a range of features, which affect how the body reacts to them.
For instance, the US Food and Drug Administration recently banned the use of partially hydrogenated oils, due to their association with adverse health outcomes.
“These features profoundly affect the biological function of fatty acids, and thus their effects on heath, in complex, incompletely understood ways,” Ludwig and his colleagues write.
It is yet another area of macronutrients into which the group would like to see more research. Indeed, they conclude with a degree of vagueness befitting their demand for further and better research: “Current evidence indicates that no specific carbohydrate-to-fat ratio in the diet is best for the general population.”
Samantha Page is a science journalist based in Spain.
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