- A study published in the journal Nature Medicine suggests consuming a low-fat diet leads to a lower overall calorie intake when compared to a low-carb diet.
- However, this may not be the best strategy for runners looking to improve their performance. Being low in a macronutrient, like fat, can lead to hitting the wall, delayed recovery, and even injury.
If you’re tweaking your diet for optimal running performance, you may find yourself down a wormhole of the seemingly never-ending debate in nutritional science: low-fat or low-carb?
A study published in the journal Nature Medicine has entered the chat by looking at 20 adults, with an average age 30, who were classified as overweight based on their body mass index.
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For two weeks, half of the group ate a plant-based, low-fat diet with a high glycemic load (in which foods are quickly digested and absorbed, causing a faster rise in blood sugar), while the other half had an animal-based, ketogenic, low-carb diet with a low glycemic load (in which foods are slowly digested and absorbed, causing a slower rise in blood sugar). Then they switched diets for two more weeks.
Researchers found that the low-fat diet offered significantly less energy intake overall, which means they took in fewer calories. When people were on the low-fat diet, they voluntarily reduced their calorie intake by about 550 to 700 calories per day compared to the low-carb weeks. And they didn’t report any differences in hunger, fullness, or satisfaction of the meals along the way.
This conclusion is contrary to current thinking, the researchers noted, which tends to knock low-fat meals because they can offer lower satiety—raising the risk of overeating. Also, eating foods with a high glycemic load can cause excess insulin production, they added, which promotes fat accumulation.
In terms of how that affected weight loss, though, it didn’t seem to make much of an impact. Despite the considerable differences in calorie intake between the diets, total weight loss after the first two weeks was similar.
So, what should endurance athletes like runners take from this study? Like many nutritional questions, the answer is “it depends,” according to Kara Hoerr, R.D.N., a dietitian who specializes in sports nutrition.
“Many people, including athletes, believe that if they follow a low-carb or low-fat diet, they’ll see desired results,” she told Bicycling. “But being low in a certain macronutrient doesn’t mean it’s necessarily better for you.”
Our bodies are designed to need a balance of fat, carbohydrates, and protein, she added, and consuming less energy doesn’t always equal improved performance. For some people, it may even lead to hitting the wall sooner.
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“[Endurance athletes] need a balance of all macronutrients in order to perform well,” Hoerr said. “Our bodies prefer carbs as a main fuel source, and we’re really efficient at using it. But we also need fat and protein to help prevent injury, help with recovery, and keep us satisfied.”
Despite the popularity of low-carb eating plans or limiting fats, she suggested that performance can suffer if athletes purposely deplete their bodies of essential macronutrients.
“Rather than focusing on what to reduce or eliminate in a diet, an athlete is better off focusing on the quality of foods consumed, such as eating complex carbohydrates, lean proteins, and healthy fats more often,” she said.
Elizabeth Millard is a freelance writer focusing on health, wellness, fitness, and food.
