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What causes obesity?

The obesity conundrum: hypotheses and hyperboles

The energy balance hypothesis vs. the endocrinological hypothesis
Calls for rigorous clinical studies

The science of obesity: what do we really know about what makes us fat? published online in the BMJ has sought to dispel our current understanding of what causes obesity.

According to the author, Gary Taubes, the history of obesity research is one of two competing hypotheses: the energy balance hypothesis and the endocrinological hypothesis.

He argues that the wrong hypothesis (energy balance hypothesis) has being touted as the correct theory and for years patients have undergone unnecessary treatment to combat their obesity, and is the reason why so many weight loss programmes fail.

“Our fundamental understanding of the aetiology of the disorder is indeed incorrect, and this is the reason for the lack of progress,” writes Taubes. “If this is true, and it certainly could be, then rectifying this aetiological misconception is absolutely critical to future progress.”


The paper states that since the 1950’s the conventional wisdom on the cause of obesity is that people become obese because they over eat and the solution is to encourage patients to burn off more calories than they consume or under eat, creating a negative energy balance. These solutions, Taubes claims, have been “remarkably ineffective”.

The observation that bariatric surgery works doesn’t answer these questions.

He claims that the endocrinological hypothesis, which claims that obesity is the results of intrinsic physiological abnormalities (eg, hormonal inbalance, altered insulin response), was proposed in mainly German language papers but was largely ignored following the end of the second world-war.

By maintain that the energy balance hypothesis was correct, Taubes claims

obesity “evolved into an eating disorder” and the physiological aspects of hunger (satiety and appetite) were the focus of research instead of the physiological (hormonal).

Gary Taubes

“The notion that obesity is not an eating disorder or an energy balance disorder, but a fat accumulation disorder - a hormonal, regulatory disorder -triggered not by energy imbalance but the quality and quantity of the carbohydrates in the diet, has been routinely dismissed ever since as unworthy of serious attention,” write Taubes.

The energy balance hypothesis maintains that the obesity epidemic can be explained by the increasing availability of calories, especially carbohydrates and sugars.

However, he argues that this does not explain whether peoples become obese because they are eating more or because the macronutrient composition of their diets is promoting fat accumulation.

“The same is true for bariatric surgery, which is now acknowledged to be a remarkably effective means of inducing long term weight loss,” write Taubes. “But does weight loss occur after surgery because of the rearrangement of the gastrointestinal tract resulting in hormonal effects that minimise appetite or directly minimise fat accumulation? Does it occur because the patient reduces total calories consumed after surgery or reduces carbohydrate calories and, specifically, refined grains and sugars? The observation that bariatric surgery works doesn’t answer these questions.”

Research shortcomings

Taubes also claims that the research conducted over the last 50 years has been inadequate and that the conclusions only indicate associations, rather than causal relations.

As a result, he calls for introduction of rigorous, well-controlled experimental trials, carried out by independent, sceptical researchers.

He claims that the medical community needs to take three necessary steps in order to make any headway into the cause/s of obesity:

  • Accept the existence of an alternative hypothesis of obesity (or multiple alternative hypotheses).
  • Refuse to accept substandard science with authors/conclusions rigorously challenged.
  • Find the resources to fund and carry out the necessary research.

“With the burden of obesity now estimated at greater than $150bn (£100bn; €118bn) a year in the US alone,” conclude Taubes. “Virtually any amount of money spent on getting nutrition research right can be defended on the basis that the long term savings to the healthcare system and to the health of individuals will offset the costs of the research by orders of magnitude.”

Gary Taubes is cofounder of the Nutrition Science Initiative and a Robert Wood Johnson Foundation Independent Investigator in Health Policy Research at the UC Berkeley School of Public Health.

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