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Welcome to Factor Impact. I am Perry Wilson. This week, we turn to the BMJ to look at one of the best studies I've ever seen in terms of measuring the metabolic effects of low carb diets,[1] and one that the media really, really misunderstood.
Picture provided by Austen Bass
To begin, here is a picture of my friend Austen.
This handsome guy lost 43 pounds on a ketogenic diet last year, and he is a strong supporter of all this. As a hard-working academician, I silently assumed that what was really happening here was that he was eating fewer calories. You can not nibble on office donuts if you do not eat carbohydrates.
Calories in, calories in. That's what weight loss is all about. You reduce calories by eating less. You increase calories by doing more exercise.
But if there is another way? This study suggests that the calories you burn can increase based on type of calories that you take in.
In other words, taking 1000 calories of carbohydrates can be worse than 1000 calories of fat because it will reduce the speed at which your body burns calories in general. Think of it as a sugar tax, with an apology to Mike Bloomberg.
The researchers took 234 overweight people and put them on a strict diet to lose 12% of their body weight; 164 made the cut. But it was only the beginning of the study.
Source: Ebbeling CA, et al[1]
With their body in total energy saving mode, these 164 participants were randomly divided into three diets: 60% carbohydrate, 40% carbohydrate or 20% carbohydrate. All diets were 20% protein, so we're essentially looking at high carbohydrate versus high fat diets.
For 20 weeks, their caloric intake has been carefully adjusted to prevent weight loss. After 20 weeks of organized meals, their total energy expenditure was assessed via water labeled twice. This is the ideal method for measuring total energy expenditure.
Now, if all the calories are equal and the weight of each is kept the same, the total energy expenditure in the three groups must be the same.
They were not.
Those in the low carbohydrate group had significantly higher total energy expenditure compared to other groups. They burned about 209 calories a day more than the carbohydrate-rich group.
This may not seem like much, but if you burn 200 extra calories a day while maintaining your caloric intake stable, you will lose about 20 pounds a year.
Elegant study, convincing results.
Have we finished here?
Not enough.
Many media reports that this study shows that low carb diets will help you lose weight.
The study does not show that. Everyone in this study lost weight before they were randomized to the diet.
Some outlets are going a bit better, claiming that the study shows that low carb diets help maintain weight.
The study does not show that either.
Remember that the weight was fully controlled in this study because the researchers controlled what the participants ate to maintain their stable weight. All people in the study, regardless of their diet, maintained their weight loss.
This study shows that diets low in carbohydrates increase the total number of calories burned. That's all. Could does this mean that low carb diets will help you lose weight? Sure. But we do not know it yet.
Always – researchers in the diet, take note: This is how you will make a rigorous study of the diet. Thanks to very meticulous experiments and measurements, we have learned that, perhaps, not all calories are created equal.
It's a good appetizer, but we are still waiting for the main course.
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