Fat, not sugar, makes mice obese

What's the news: Fat, not sugar, makes mice obese.

Why should we believe it: This news is based on a study published at the start of this year, in January 20233, by scientists at the Université catholique de Louvain in Brussels, Belgium.

In this study, scientists looked at 50 lab mice, and divided the mice into four groups. Each group got the same number of calories, with a different macronutrient breakdown:

1. Low fat, low sugar

2. High sugar

3. High fat, high sugar

4. High fat

The results were surprising but clear: The most weight gain, and the most fat gain, came in the high-fat group. This was higher than in the high-fat-high-sugar group, which was higher than the high-sugar group.

In other words, fat, not sugar, made for fat mice. Fat, not sugar, also contributed most to inflammation, insulin resistance, and a drop in diversity of gut microbiota.

Why is this a big deal: We know that obesity is bad for health, and there’s evidence that obesity drives aging as well. What we don’t know, mindboggling though it may be, is what's been driving an increase in obesity in humans.

Just as important, we still don't have a convincing picture of what kind of diet is optimal — both on a broad scale and individually — for losing weight. Keto? Paleo? Vegan? All ice cream, all the time? The present study adds another data point to this complex debate, and it shows that, in mice at least, a high fat load is not good for health.

So what specifically can you do now: Your Long Youthspan editor is not in the habit of advising lifestyle changes based on the latest mouse study. It’s very possible that mouse results won’t translate to humans. That holds for the present study as well.

For now, just keep this study in mind, and slowly and carefully pull it out if you're ever faced with a keto fanatic who wants to pressure you, and who claims that the science on sugar v. fat is clear.