There is a lot of buzz about Dr. Stephan Guyenet’s article on The Carbohydrate Hypothesis of Obesity.
This is one of my favorite blogs and I have been reading it for years. It is quite heavy on the science, but if you are a biology and nutrition geek like me, then I highly recommend you subscribe.
I would like to extract the key points from this very important article and present some of my own thoughts.
What this article evaluates is the hypothesis that excess carbohydrates cause obesity, largely promoted by Gary Taubes in his book Good Calories, Bad Calories.
The mechanism proposed in the carbohydrate hypothesis, is that excess carbohydrates cause elevated levels of insulin, which encourage fat accumulation in fat cells.
This is something that makes sense on the level of the fat cells, because insulin encourages them to store fat and prevents them from releasing fat, by controlling particular enzymes.
This is a biochemical fact, and this is how insulin affects fat cells, at least in the short term such as after a meal.
I have to admit that the carbohydrate hypothesis is something I’ve partly believed in, although I do believe that the type of carbohydrate is critical, where sugar and refined wheat are by far the worst.
The key points from the article
The fact that low-carbohydrate diets are effective for weight loss in obese people is something Dr. Guyenet agrees on, but he does not believe that the mechanism for this effect is lowered insulin levels.
Some points made about insulin, supported with research:
- When insulin is secreted, a satiety factor called amylin is secreted too.
- High-carbohydrate meals cause greater satiety and less subsequent food intake than high-fat meals, when calories and protein are controlled.
- Low-carb, high-protein meals can stimulate as much insulin as high-carb meals.
- Amount of insulin secretion is correlated with increased satiety.
- Insulin injected into brains of monkeys makes them lose fat.
- Higher fasting insulin is associated with increased energy expenditure.
- Different carb:fat ratios don’t influence energy expenditure, neither in the short or long term.
- Insulin resistant obese people release more fatty acids from their fat cells than lean people.
- Obese people expend more energy than lean people, but also eat more calories.
There are many genetic defects linked to obesity, and all of them involve the regulatory system in the brain, not insulin or insulin signaling.
Many cultures eat a very high-carb diet and are lean and healthy. These populations do not gain weight until they adopt a more western diet, including sugar, wheat, industrial oils and processed food.
Since the turn of the 20th century, the only macronutrient that has increased as a percentage of calories is fat, not carbohydrate. Obesity was rare around the year 1900 despite the fact that 57% of calories came from carbohydrates.
My thoughts about the whole thing
I believe Dr. Stephan Guyenet is one of those in the world who knows the most about obesity. Professionally, he studies the neurobiology of body fat regulation and is an expert on the subject.
He believes that food reward is much more likely to be the cause of obesity, where the brain is the primary regulator of food intake.
I must admit that the insulin hypothesis is something I’ve partly believed in, and it’s something I’ve talked about on this blog before.
I was wrong, and I stand corrected.
There is something else in the modern diet and lifestyle that causes obesity, sugar and wheat being likely suspects. Not because of their effect on insulin but because they cause a massive “reward” in the brain that can lead to addiction and overeating.
The fact is that obesity is a very complex disorder with multiple causes, where insulin is less important than previously thought.
I’d like to mention again, that this does not change the fact that low-carbohydrate diets are very effective at causing weight loss in overweight people.
It is a fact that they do, but people disagree on the reason why.