Carbs...tasty, tasty, carbs... Photo Credit: Pixabay

Guest Post: Low carb diets vs. low fat diets

Dr. Christopher Labos is a Montreal physician and science communicator. He is co-host of the Body of Evidence podcast and a regular contributor to Montreal Gazette. Dr. Labos writes about what reproducible evidence has to say on important scientific and medical concepts. You can follow him on Twitter @drlabos 

Key Vocabulary: nutrients, metabolic pathways (metabolism), calories, fat, carbohydrate, randomized trial, hypothesis

Next Generation Science Standards:

  • MS-ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

Many people, especially TV celebrities with diet books to sell, will tell you that sugar is bad for you and the reason why so many people are overweight. They will then go on to tell you that you can lose weight by switching sugar for fat. The promise is that you can lose weight without cutting calories because a calorie from sugar is not the same as a calorie from fat.

Their theory is that the body handles sugar and fat differently. That is true. Different nutrients are handled by different metabolic pathways. But the question becomes if you take your current diet and swap out sugary foods for fatty foods, will you lose weight (assuming the total number of calories remains the same)?

Eat your fruits and veggies! Photo Credit: Wikipedia

The answer is actually no. First off, the existing evidence supporting low carb over low-fat diets is fairly weak. While there seems to be a small edge to low-carb diets at six months, that advantage disappears by one year. Long term, the diets appear to be roughly similar to weight loss.

However, a new study recently came out that adds more evidence against this idea. Randomized trials in nutrition research are tough, largely because it is very hard to get people to stick to a diet and hard to know whether they are snacking or cheating when they are not supposed to. The only way to make it work would be to confine a group of volunteers and feed them only what you want to study. Well, that is exactly what a group of researchers did. They recruited 17 volunteers and housed them for two months, giving them first a regular high carb diet and then comparing it against the proposed low carb diet, while keeping total calories the same.

While the study was small with only 17 people, it is impressive that they convinced that many to give up two months of their lives in the name of science. If the “insulin hypothesis” were true, these people would have lost substantial weight when they were switched off the carbs. The hypothesis goes that eating sugar drives up insulin, and insulin makes you store more fat. Therefore, if you eat less sugar, your body will burn more fat.

Sadly, the theory didn’t pan out. In this new study, the 17 volunteers did have a drop in their insulin levels when they made the switch to the low-carb diets, but their bodies didn’t seem to burn any extra fat and they didn’t lose any meaningful amount weight. In fact, fat loss slowed slightly when people were put on the low-carb diet. Ultimately, despite minor differences in the groups, going on the low carb diet didn’t have much of an effect.
Dr. Christopher Labos, MD

The insulin hypothesis sounds like a promising idea. And of course, sugar is bad for you, and yes, you should be eating less of it. But it seems clear that if your total calorie intake stays the same, you won’t be losing much weight. It appears that a calorie is a calorie, despite what some health gurus have claimed.

Swapping out one form of junk food for another is never a good idea. In the 1980s and ’90s, people looking for low-fat foods, eagerly ate up products that were full of sugar. It would be equally bad now if we flipped to the other extreme and blindly started buying sugar-free food that is high in fat.

It would be best if we could eat less in general and focus on foods that are both low fat and low sugar.

You may have heard of these foods. They are called vegetables.

This article first appeared in the Montreal Gazette.

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