Todd Miller, Ph.D. January 16, 2018

Cutting carbs has quickly become one of the most popular strategies for losing weight. The reason for this is largely due to a misunderstanding of what causes weight gain in the first place, coupled with a misinterpretation of scientific research on the topic of carbohydrate metabolism.  But, is cutting carbs actually essential for achieving fat loss?

If we consider what actually happens to the human body when a person eliminates or limits carbs from the diet, it is easy see why many of us may fall prey to the common misconception that carbs are the central cause of all weight gain. Where carbs go, water follows.

Carbs are stored in the muscles and liver as a compound called glycogen. Glycogen is released into the bloodstream as glucose to fuel the brain, and is metabolized in the muscles for energy.     Glycogen is hydrophilic, meaning it attracts water.  If we stop eating carbohydrate, or dramatically limit its intake, glycogen stored in the muscle and liver will decrease as it is burned for energy.  As these glycogen levels fall, so does water in these tissues.  As a result, weight falls off rapidly when carbs are eliminated from the diet.

However, since most of this weight loss is from water loss, fat mass often remains relatively unchanged, at least for the short term.  When carbs are added back into the diet, glycogen stores go up, along with water in the muscle and liver, which leads to rapid weight gain. So, it is easy to see why we might blame carbohydrates as the central problem.

In fact, we work with many athletes who compete in sports classed by competitor weight (ex: mixed martial arts, rowing, wrestling, etc). Often times, eliminating carbs is the first thing they’ll do to lose weight.  Again, these rapid losses are almost all water weight, and do not offer long-term results.

Assuming a person were to stay on a no-carb or carb-restricted diet, it is likely that he/she would eventually experience fat loss.    However, this is simply due to a decrease in calorie consumption.   Individuals who completely cut out any given macronutrient from the diet, will in turn dramatically limit the number of foods they can could eat, and as a result, will naturally eat less.

I am reminded of a friend in college who decided to go on a no-carb diet back when the Atkins diet was a popular weight loss trend.  Every time he had pizza for dinner, he would only eat the cheese and pepperoni – no crust.   He did this on a regular basis, and sure enough, started to lose weight. He then came to the (illogical) conclusion that carbs from pizza crust were the primary culprit contributing to his weight gain.

But, the reality is, eating the cheese and pepperoni only simply resulted in consuming fewer calories.  It is likely that he would have seen similar results had he eaten only the crust and no cheese or pepperoni. Both tactics render the same result – fewer total calories eaten.

The most recent version of the low carb craze is the Ketogenic Diet (or Keto Diet).  This diet requires one to eat roughly 70 percent of calories from fat, with a very small amount coming from carbohydrates, and the remainder from protein.  In the most well-controlled studies comparing the effectiveness of a Ketogenic Diet versus a normal carbohydrate diet for fat loss, there is no difference in fat loss when the calories are held constant between the two conditions.

In short, the main thing that drives fat loss is creating a caloric deficit – not whether you eat mostly fat or mostly carbs.     This is not to say that Ketogenic diets are not effective.  They often work for fat loss, but this is primarily because you tend to eat less on Ketogenic diets due to their ability to stave off hunger, thereby creating a calorie deficit.

Many different approaches can be effective in regards to fat loss.  However, any approach that works, does so because it fosters a caloric deficit, which can be achieved by eating a variety of foods.

Carbohydrates, per se, are not responsible for causing weight gain, and there is little empirical evidence to support that common misconception. As it has always been the case, when the average number of calories you eat is in balance with the number of calories burned, weight remains stable, and there is generally no increase in body fat. This truth demonstrates that total food intake is the main factor affecting weight gain – or loss – not the type of foods a person eats or doesn’t eat.

The contents of the above article are not a substitute for the advice of your healthcare professional. If you have been advised to be on any specialized diet, please continue as directed.