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Is diet soda bad for us? An evolutionary perspective.

A recent paper reports that "Diet Soft Drink Consumption is Associated with an Increased Risk of Vascular Events in the Northern Manhattan Study." The correlation persisted even after they corrected for "age, sex, race/ethnicity, education, smoking, physical activity, alcohol consumption, BMI, daily calories, consumption of protein, carbohydrates, total fat, saturated fat, and sodium... and this persisted after controlling further for the metabolic syndrome, peripheral vascular disease, diabetes, cardiac disease, hypertension, and hypercholesterolemia."

Previous studies have found correlations between diet soft drink consumption and other health problems. What's going on? A specific artificial sweetener could have some specific negative effect. But could the sweet taste itself cause health problems? An evolutionary perspective suggests that it could.

Tradeoffs between current and future reproduction (or fertility vs. longevity) are common. Given such tradeoffs, will natural selection favor reproducing now (sacrificing some longevity) or later?

If conditions are good, so that the overall population is growing, it's better to reproduce now, even if that means a shorter life and fewer total offspring. By the time slow-reproducers get around to reproducing, you may be dead, but your many children will be having children.

But if conditions are bad, so that the overall population is decreasing, you may be able to increase your proportional representation in future generations by saving your strength and reproducing later. Even if you have fewer total offspring, you'll be adding them to a much smaller gene pool then if you reproduced before the crash.

So, how do our bodies tell whether the overall population is likely to increase or decrease? If we're eating fruit, rather than leaves, times must be good. But that means the population is likely to increase. So throw the "fertility vs. longevity switch" to the fertility position, whatever the long-term consequences for health.

This hypothesis is consistent with the increased longevity of animals on restricted diets and especially with the reversal of that effect by food odors. I've discussed this in more detail in earlier posts.

One result in this week's paper seems to contradict the "sweet-tasting food is bad for you" hypothesis. however. They found that "there was no increased risk of vascular events associated with regular soft drinks." I think "increased" meant "increased relative to what you would expect from the calories in those drinks." If so, then calories plus sweet taste may be no worse than calories alone.

Comments

Ford,

This is some really cool stuff. I am confused by the last two sentences though.

My interpretation of the paper (after downloading and reading it) is that diet soft drinks significantly increase an individual's risk for vascular events whereas regular soft drinks do not.

Maybe I am missing something, but I don't understand why that could mean that "calories plus sweet taste may be no worse than calories alone."

Jason,

You are right. My statement didn't make sense. The lack of correlation between vascular events and regular soft drinks tends to undermine the hypothesis that sweet tastes always trigger adverse physiological changes. Maybe people drinking sugared soft drinks drink less, worried about calories? We need controlled experiments, not just surveys of what people remember and admit to eating and drinking. I'm hoping to do such experiments, but not with people.

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