Rethinking the Low-Carb Diet for Health and Body Composition

What happens when you go into ketosis?

By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital

Low-carb—particularly ketogenic—diets are all the rage these days. Are they beneficial in the long term, though? Professor Anding explores the function of carbohydrates and what happens when you remove them from your diet.

Close up of bread being cut on cutting board
Rather than giving up an entire food group, modify the type of carbohydrates that you eat, staying away from simple starches and selecting whole grains instead. Photo by VGstockstudio / Shutterstock

Effects of a Low-Carb Diet

Carbohydrates are central to the optimum functioning of the human body. When people go on a low-carb diet, they often become irritable, fatigued, and lethargic because they are missing this vital nutrient. 

The primary function of carbohydrates is to serve as an energy source. It is the high-octane fuel that your body prefers for your central nervous system. 

A carbohydrate has four calories per gram. Fat, by contrast, has nine calories per gram. In terms of weight management, then, carbohydrates are actually preferable to fat.

Carbohydrate prevents ketosis, which is when your body burns fat for energy instead of sugar. Fat can provide a valuable supply of energy, but carbohydrate is needed to burn that fat completely. In the absence of carbohydrate, the fat breakdown is incomplete and something called “ketone bodies” form. 

Think of the gasoline in your car. If you have gasoline in your car that’s burning appropriately—that’s a combination of fat and carbohydrate—you’re going to get the energy to fuel your car. In the absence of the right kind of fuel, you end up getting a waste product. 

The waste product of fat metabolism is ketones, which is like the carbon monoxide that comes out of the tailpipe. It’s the incomplete burning of that fuel that leads to an accumulation of ketones that are not great for your overall health. They can cause nausea, dehydration, headaches, and brain fog.

Protein and Ketosis

An often forgotten role of carbohydrates is sparing protein. Carbohydrates spare protein so it can perform its own unique function. There is no interchange. 

Carbohydrate protects, or bodyguards, protein so that it can build and repair tissue. When there’s inadequate energy in the form of carbohydrate, some protein will be broken down to provide the energy needed for basal metabolic rate—the calories you burn at rest. 

Think about it this way. With inadequate amounts of carbohydrate, you must turn to your plan B to provide energy, and your plan B is going to be protein. 

The reason that protein is broken down and not fat is that protein can serve as a source of carbohydrate. Protein can be sent to the liver and turned into glucose if your carbohydrate intake is too low. This loss of protein means that you lose muscle mass, which impacts your overall body composition.

Ketogenic Diets Long-Term

In the short term, a low-carb, or ketogenic diet, can reduce blood sugar and offer benefits for weight-control, diabetes, and epilepsy. However, most doctors and nutritionists do not recommend a ketogenic diet in the long-term as it can lead to nutritional deficiencies.

Rather than depriving yourself of an entire food group, Professor Anding recommends seeking out the healthy carbs found in whole grains, which power your body throughout the day and provide you with fiber which is needed for optimal digestion.

At the same time—especially if you’re concerned about your weight or glucose levels—you should avoid refined carbs such as white bread/pasta and foods and drinks high in sugar, including “diet” products which often contain hidden unhealthy ingredients such as high-fructose corn syrup.

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.