A Hot Debate About Insulin and Sugar and Obesity

JAMA Internal Medicine has just published the latest chapter in a hot debate about insulin and sugar as culprits responsible for obesity. David Ludwig and Cara Ebbeling present the prosecution’s case. A spike in highly processed carbs – like refined starches and sugar – is giving us a high glycemic load, they say. And in turn, that glycemic load stimulates insulin production. The end result? Metabolic dysfunction, increased fat storage, and, voilà, a spike in obesity.

An Appealing Story

It’s an excellent, appealing story. Not only that, it gave Ludwig the basis for a bestselling diet book. It also has the advantage of offering a less dogmatic alternative to Robert Lustig’s sugar-is-toxic creed. It takes a broader view than the obsessive focus on sugar that is so dominant in policymaking right now.

The carbohydrate-insulin model (CIM) is simply a better framework for understanding obesity, say Ludwig and Ebbeling. They do concede that it needs more research. But even so, it’s more consistent with current science than outmoded thinking about calories in and calories out.

Not So Fast

Kevin Hall, Stephan Guyenet, and Rudolph Leibel beg to differ. The CIM doesn’t fully line up with current obesity science, they say. Although refined carbs may contribute to obesity, the CIM doesn’t explain all the underlying pathways. Insulin signaling might be a part of the problem. But it’s not the whole story.

To the contrary, they submit that obesity has many different forms and dimensions. Many factors contribute. Genetic, metabolic, hormonal, psychological, behavioral, environmental, economic, and social factors all come into play. In short, the CIM  is incomplete and inconsistent with current evidence.

So What?

If this were just an academic debate, it would not matter all that much. Academics could continue arguing about insulin and sugar and obesity for yet another century. We could debate about sugars and refined starches. But the fact is that policymakers are acting as if this debate were already resolved. All over the world, sugar taxes have become the holy grail to stop the spiraling global pandemic of obesity. Never mind that we’ve yet to see any impact on obesity prevalence from such taxes.

Taxing sugar cuts sugar consumption. And if you have faith in the creed that sugar is toxic, then surely that will be enough to stop the pandemic in its tracks. Alas, we wish it were that simple.

At the end of the day, though, we agree on one point, articulated by all five authors. Current science doesn’t tell the whole story. Research to resolve this hot debate should be a priority. Shooting in the dark is a lousy alternative.

Click here for the paper by Ludwig and Ebbeling, and here for the paper by Hall, Guyenet, and Leibel.

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July 5, 2018

3 Responses to “A Hot Debate About Insulin and Sugar and Obesity”

  1. July 05, 2018 at 9:35 am, David Ludwig said:

    Ted, your interpretation of the CIM, and policy inferences, are misleading. First off, even if the CIM were simply about sugar, it’s wildly unrealistic to expect any single, haphazardly enacted policy measure to change obesity prevalence in the short term. More relevantly, we have clearly argued that sugar isn’t the only issue: the CIM address all high glycemic load carbohydrates. From this perspective, the refined starches that flooded our diet during the low-fat diet years are potentially a bigger problem than sugar. Most refined starches raise insulin secretion more than sucrose … and we eat a lot more of them.

    Finally, I would would point out that the conventional “calories in, calories out” model (not the CIM) has been driving policy for 50 years, witness the low fat diet, brought to you courtesy of “calorie balance” considerations.

    • July 05, 2018 at 10:25 am, Ted said:

      Thanks, David, for making some excellent points. I agree completely about the limited effectiveness of haphazard policy measures. And thanks for clarifying about the importance of a broader focus on high glycemic carbs. I agree that we need to focus on more than sugar alone. And finally, you are absolutely right that simplistic calorie accounting has been dominant in policymaking, leading us to “solutions” that have solved very little.

      Again, thanks!

  2. July 05, 2018 at 11:44 am, John DiTraglia said:

    I think the Ludwig-Lustig-sugar-carbs bandwagon has already launched 100 ships and it’s premature and will look as silly as so many dogmas seem to do in this business. I think the experts should always first admit that the obesity epidemic is a riddle, wrapped in a mystery, inside an enigma.