Does Sugar Make Dietary Fat Less OK?

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I have defended dietary fat as healthy in many blog posts, including

But there is one circumstance in which dietary fat might not be so great: if you are still eating sugar. In last week's post, "Heidi Turner, Michael Schwartz and Kristen Domonell on How Bad Sugar Is" I quote this:

Schwartz agrees that sugar can cause major health problems, but says it isn’t acting alone. The most potent way to activate the brain’s reward system is actually by combining sugar with fat, he says. And much of the American diet contains both of these components.

There is a claim here about complementarity in badness: that is, in the presence of sugar, dietary fat is worse than in the absence of sugar. I take the view that in the absence of sugar, dietary fat—other than the big mistake of transfat—is quite healthy. But it is logically possible that dietary fat combined too close in time to sugar is unhealthy. Let me spin out a possible theory. I should say first that I am not really persuaded by the "overwhelmingly rewarding" theory that Michael Schwartz is putting forward. Sugar is extremely rewarding. Fat is extremely rewarding. Is the combination of sugar and fat that much more rewarding than sugar in combination with nonfat foods or fat in combination with nonsugar foods?

Instead, let discuss things from the standpoint of the satiation to calorie ratio I talk about in "Letting Go of Sugar." Dietary fat by itself, or in combination with other foods low on the insulin index (see "Forget Calorie Counting; It's the Insulin Index, Stupid") is quite satiating: it will make you feel full quite fast. But sugar has a negative satiation to calorie ratio: it makes you feel less full. So add enough sugar to your dietary fat, and the dietary fat's normal tendency to make you feel full will be neutralized. 

The idea that sugar neutralizes the tendency of dietary fat to make you feel full still doesn't seem to make dietary fat any worse than anything else combined with sugar. But what if, in addition to the mechanisms that normally make dietary fat satiation, there is a volumetric mechanism that makes you full if there is a high volume of food in your stomach. It would make sense that sugar can neutralize some mechanisms that make you feel full, but it can't neutralize the volumetric mechanism. But dietary fat doesn't have a lot of volume per calorie, so if the normal mechanism that makes dietary fat so very satiating is neutralized, there isn't a volumetric backup mechanism for fat. Sugar gets past the main safeguard that makes you not want to overeat dietary fat and that's it. 

Solution? Don't eat sugar. See "Letting Go of Sugar" for how to get there. Sugar is bad whether or not it is combined with dietary fat. Even on the theory above, dietary fat is only bad when combined with sugar.


Don't miss these other posts on diet and health and on fighting obesity:

Also see the last section of "Five Books That Have Changed My Life" and the podcast "Miles Kimball Explains to Tracy Alloway and Joe Weisenthal Why Losing Weight Is Like Defeating Inflation." If you want to know how I got interested in diet and health and fighting obesity and a little more about my own experience with weight gain and weight loss, see my post "A Barycentric Autobiography."