Guyenet, Taubes and why low carb works


After the recent fireworks at AHS, perhaps this should not come as a surprise. Neurobiologist and popular blogger Stephan Guyenet has posted on why he does not believe in (refined) carbohydrates as an important cause of obesity. Although he does acknowledge that a low carb diet is effective for making you lose weight.

Sound complicated? It is:

Whole Health Source: The Carbohydrate Hypothesis of Obesity – a Critical Examination

This makes me think of a common saying regarding forests and trees (thus the illustration). Let’s untangle this mess.

The basic premise

The Carbohydrate Hypothesis, as attacked by Guyenet, looks basically like this:

Excessive amounts of carbohydrates (especially refined carbs / sugar) increases insulin and results in fat gain.

Guyenets argues in his post that carbs are not necessarily the cause of increased insulin, and insulin certainly do not result in gaining weight (maybe the opposite!). Basically he says that while low carb works, the theory to explain it is wrong.

However, as every doctor who has ever treated diabetics with insulin (and their patients) probably knows, injecting insulin certainly does tends to increase fat gain. And in untreated type 1 diabetics, with no insulin, weight plummets. Guyenet does not mention that.

Thin people usually have low insulin levels, obese people usually have high levels of insulin. Guyenet does not believe that is significant.

My answer to Guyenet’s post

Very interesting post (as always), but several surprisingly unconvincing arguments.

First of all: You state that low carb diets do indeed work well for weight loss most of the time, and that you see that as a fact. Kudos to you for acknowledging it. However, you can’t say for sure why they work, if not through insulin, so maybe we should not rush to conclusions yet.

You also claim that obesity and metabolism researchers do not take the carbohydrate theory seriously. Well, as they have so far failed spectacularly to come up with anything useful for obesity I’m not sure that is a bad thing.

In the face of massively increasing obesity rates there is only one drug approved in Europe (where I work as a doctor treating obese patients), orlistat, and everyone pretty much agrees that it sucks. The only solution proposed is to cut away healthy stomachs to stop fat people from eating. Yikes.

The failure of obesity and metabolism researchers (however smart) during the last decades is of epic proportions. It makes the Hindenburg look like a success story. Please don’t tell me we should care about what they believe in.

On to your three so called “falsifications”:


You argue that leptin is more important than insulin in obesity. Take a look at Robert Lustig’s lecture during AHS. Hyperinsulinemia results in leptin resistance.

Problem solved. Moving on:


Insulin results in fat being pushed into fat cells BUT insulin also signals satiety in the brain… problem? No. Like most hormones (cortisol is a good example) insulin has short term and long term effects:

Short term it increases satiety in the brain. Makes perfect sense as it normally means that we just ate.

Long term hyperinsulinemia, on the other hand, increases fat storage and makes us eat more. At least partly through the resulting leptin resistance, like professor Lustig pointed out.

Again, problem solved. Nothing “falsified”.


You claim that not just (especially refined) carbohydrates increase insulin, so does protein to some degree. Sure. But we all need protein and low carb diets are mainly about switching carbs to fat. Carbs release lots of insulin, fats do not.

There are plenty of studies showing that low carb diets drastically reduce insulin levels during the entire day. If you’d like references just say so.

Again, nothing falsified.

To summarize:
Of course not all carbs are evil all the time. But refined carbs (sugar, easily digested starch) can be a huge problem for sensitive people (obese, diabetics). It seems we agree on that, as well as that low carb diets can be most helpful in those conditions.

What is really being questioned here is the explanation behind the way the world works. And perhaps it is not quite so simple as Taubes and others once thought.

However, if we complicate the theory just a little bit it still works fine. Let’s not rush to prematurely “falsify” a working hypothesis when we have nothing better to replace it with.


Whether we bother to add the step with leptin or not, this still seems to be true:

Excessive amounts of carbohydrates (especially refined carbs / sugar) increases insulin and results in fat gain.

Of course, what “excessive amounts” means vary from person to person, and it also depend on what carbs we are talking about. Two examples: Young fit men often tolerate a lot of carbs, even sugar, without gaining much weight, but middle-aged obese women with type 2 diabetes do not.

Bottom line

Some very smart people disagree why low carb works. But we all seem to agree that it does work.


AHS showdown: Gary Taubes vs Stephan Guyenet

The American obesity epidemic 1989 – 2010

Why Americans are obese: Nonfat yogurt

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