In a recent “Viewpoint” (i.e., opinion) article for JAMA, David Ludwig and Mark Friedman compare and contrast prevailing and alternative models of obesity.
The prevailing model:
Voluntary changes in calorie intake predictably produce short-term weight change, suggesting the possibility of conscious control of body weight over the long term.
Evidence exists, though, that contradicts the prevailing model:
However, feeding studies demonstrate that changes in energy balance produce biological adaptations that antagonize ongoing weight loss or gain. For instance, in a study in which 41 lean or obese research participants were underfed or overfed to achieve 10% to 20% weight change, energy expenditure decreased or increased, respectively.
That is, the body tends to defend its baseline body weight.
On the way toward forming an alternative model:
The body has a continuous energy requirement, and for this reason, the concentration of major metabolic fuels—glucose, nonesterified fatty acids, and ketones—is tightly controlled…
An acute decrease in the circulating concentration or oxidation of these fuels provokes intense hunger and food intake. Conversely, pharmacological manipulations that increase metabolic fuel availability…lower food intake.
States of increased insulin action, such as excessive insulin treatment in diabetes and insulinoma, predictably cause weight gain, whereas decreased insulin action (e.g., insulin omission in type 1 diabetes) results in weight loss.
Evidence for an alternative model based on animal studies:
Rats fed high vs low glycemic index diets developed hyperinsulinemia, increased expression of fatty acid synthase in fat tissue, and greater incorporation of glucose into lipids—metabolic abnormalities that predispose to excessive fat deposition.When the high glycemic index animals were food-restricted to prevent excessive weight gain, they still gained substantially more fat (70%) than the low glycemic index animals and also exhibited adverse changes in cardiovascular disease risk factors.
The authors conclude that focusing on diet composition instead of on total calories exclusively, may facilitate weight loss. They are careful to emphasize that this is a long-term strategy for weight loss and maintenance since focusing solely on calories likely is a strategy “destined to fail over the long term for most people in an environment of unlimited food availability.”
…qualitative aspects of diet may improve metabolic function and increase circulating concentrations of metabolic fuels independent of calorie content. One approach aims to reduce insulin secretion with a low glycemic index or a low-carbohydrate diet.
But wait—calories still count:
Ultimately, weight loss requires consuming fewer calories than expended. A common interpretation of this thermodynamic principle deemphasizes the importance of dietary composition and instead places focus on behavioral methods [Lauren’s insertion: that is, willpower] to establish a negative energy balance.
The quality of calories counts, too:
According to an alternative view, the metabolic effects of refined carbohydrate (consumed in greater amounts now than in the 1970s, with adoption of the low-fat diet) and other environmental factors cause the adipocyte to take in, store, and trap too many calories.
Source: Ludwig, D. S. & Friedman, M. I. (2014). Increasing adiposity: Consequence or cause of overeating? JAMA [Epub ahead of print].