Keen to try keto? Read this

There are a whole lot of very enthusiastic advocates for the low-carb, high-fat diet, looks at whether the scientific evidence stacks up.

There’s a lot of competition for the most contentious issue in weight loss, but I’d have to give the nod to ketogenic diets. Now a study about them sheds some interesting new light – although I’m not holding out hope for kumbaya.

First though, a brief overview of the theory of ketogenic diets. When you eat carbohydrates, your body processes them with insulin, which shuttles blood glucose into fat stores, leaving you hungry. If you don’t eat many carbs, your body starts running on ketones, which your liver manufactures from fat – less hunger, less fat accumulation. Or that’s the theory, at any rate.

It’s important to keep in mind that nothing, including keto diets, can defeat the calorie balance equation: To lose weight, you have to burn more calories than you absorb.

But there are two mechanisms by which a keto diet might help you do that: It could leave you satiated on fewer calories, so you take in less, and it could increase the rate at which your body burns energy, so you expend more. Does keto actually do those things?

Let’s take appetite first, which brings us back to that interesting new study. It’s by the US National Institutes of Health’s (NIH) Kevin Hall, the same scientist who found that people eating ultraprocessed food ate 500 calories more a day than people eating a diet of whole-ish foods. This time, he compared a keto diet to a low-fat, high-carb plant-based diet.

If you’re of a certain age, you may recall that low-fat diets have their own theory, about which much was made back in the 1990s.

Because fat is calorie-dense – 9 calories per gram versus 4 for carbs and protein – high-fat diets lead to overconsumption. Hall’s study wanted to test the battling theories by comparing the diets head-to-head.

Twenty subjects, inpatients at an NIH facility so all their consumption could be monitored, were fed either the keto diet or the low-fat diet for two weeks, and then switched over to the other. (These studies are very expensive, which is why they tend to be small and short.)

Which diet led to less consumption? Drumroll, please.

The low-fat. By a lot: nearly 700 calories a day. This, despite the fact that insulin levels on the lowfat diet were, Hall told me, ‘‘through the roof’’.

The low-fat group also lost a little more fat (only about a pound, not enough for statistical significance). The keto group lost more fat-free mass, but Hall points out that a big component of that is water, which you always lose when you cut carbs.

But wait! This is not the last nail in the coffin of keto satiety. Hall made a point of highlighting the fact that, on the keto diet, consumption dropped by 300 daily calories in the second week, possibly because of a satiety effect kicking in.

Would it have dropped more had the study gone longer? There’s no way to know, but it’s certainly possible.

A 2015 meta-analysis of studies of satiety on keto

If keto works for you, I’m delighted! If it doesn’t, you’re not alone.