Linking Nutrition and Health Part 2: Obesity and Overeating

Good nutrition brings good health. That much is easy. Overeating begets obesity? Not so fast, said Lee Kaplan as he opened the 31st Harvard Blackburn Course in Obesity Medicine yesterday. This is a case of an association that is so tight that many people take it for granted. But linking nutrition to health has many pitfalls. And as it happens, the evidence is stronger for reverse causation. In other words, Kaplan said, the data is stronger to say that obesity causes overeating.

Environmental Drivers of Obesity

Kaplan described the environmental factors that may be driving the present surge in obesity. Changes in the food supply seem to be affecting signals between the gut and brain that regulate the biological drive to eat. Decreased physical activity seems to be affecting muscle function and signalling to the brain in a way that also disturbs metabolic balance.

Chronic stress and distress adds to these disturbances, as do medications that cause weight gain. And thus, the brain starts working to defend a higher set point for the body’s fat mass. Obesity – that higher set point for fat mass – triggers overeating if the fat mass drops below that set point.

This idea is not entirely new. William Bennett described it in a 1995 NEJM editorial. Deborah Cohen and Thomas Farley sketched it out (albeit in somewhat different terms) in a 2008 paper. David Ludwig and Mark Friedman made the point in a 2014 JAMA viewpoint.

Folk Beliefs and Resistance

Despite all of the analysis and evidence pointing in the opposite direction, popular opinion persists in the belief that overeating is the root cause of obesity. Boyd Swinburn did quite a media tour in 2009 with the headline message being: Overeating to Blame for U.S. Obesity Epidemic. And that’s message that sticks in public awareness.

But perhaps this will change. The public is starting to understand that diets don’t cure obesity. Simply taking calories out of the food supply will not cure obesity that has already taken root in 40% of the population. But to bring the public along, we need to answer the obvious question. What will solve the problem? Kaplan and other researchers have some pretty good leads.

But for now, we have more questions than answers.

Click here, here, and here for three viewpoints on why obesity causes overeating and not vice versa. For Part 1 of this series on the pitfalls of links between nutrition and health, click here.

Kings Feast, painting by Pavel Filonov / WikiArt

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June 15, 2018