How can Restricted Diets Affect Runners

The most popular diet trends in the past few years have been low-carb diet, Keto diet and one of the most popular currently is the intermittent fasting. These are very restricted diets that most people are using to lose weight and body fat. 

Low-Carb Diet:
10-30% Carbs
30-40% Fat
40-50% Protein

Ketogenic Diet:
75% Fat
20% Protein
5% Carbs

Intermittent Fasting:
5:2 Fasting- Normal diet for 5 days and fasting for 2 days/week (500-600 calories).
18:6 Fasting daily- Fasting for 18 hours/day and limited eating time 6 hours/day.
16:8 Fasting daily- Fasting for 16 hours/day and limited eating time 8 hours/day.
14:10 Fasting daily (more balanced)- Fasting for 14 hours/day and limited eating time 10 hours/day.

Can intermittent fasting help runners?
Intermittent fasting can help lose weight and body fat. To train on an empty stomach can work for some runners but only for short distance and low-intensity runs. Some people can sustain intermittent fasting, but to follow a more balanced schedule diet is healthier to support metabolic and hormone health, better sleep, avoid mood swings, support energy levels and stamina. Intermittent fasting for a short period can help with weight loss for some people, while others tend to overeat during the eating time. For runners, intermittent fasting and restricted diets have shown to have mostly negative side effects. If we look at the worldwide top runners, short or long-distance runners, none of them are following restricted diets. 

Intermittent fasting diet and restricted diets side effects for runners

  • Fasting before a long-distance run could result in muscle wasting
  • May increase the risk of illness
  • Reduce training intensity
  • Compromise sleep
  • Negatively affect mood
  • Compromise recovery
  • Low levels of glucose- the brain’s major energy source
  • Increase the risk of overeating later in the day

Dangers of Running After a Fast

  • Excessive sweating
  • Muscle control issues
  • Severe fatigue
  • Light headedness
  • Nausea
  • Vomiting
  • Dizziness
  • Trouble breathing

Side Effects of Fasting Post-Run

After finishing a run, whether you are fasting or not, your body needs to refuel with the proper nutrients. The body needs some carbs and protein 4:1 or 3:1 (depending on the distance and intensity) to kick start the metabolism for recovery and refuel your muscles for repair and recovery.

Benefits of Eating Before Running

  • Muscles well fueled for performance
  • Can improve post-run recovery
  • Allows for harder or longer runs
  • Increases total calorie burn of the run
  • Helps to prevent overtraining by stabilizing the hormones
  • Increases the energy levels

People who run and train regularly need carbohydrates for fuel, as carbs are most easily metabolized into energy by the body. Runners need regular fuel to perform their best. Your blood sugar control, mental clarity (brain needs glucose), and energy levels can all be negatively affected with intermittent fasting.

If weight loss is a goal, it is better for runners to create a small calorie deficit each day versus intermittent fasting. This can help meet the weight loss goals while not compromising the runs.

By eating a well-planned, clean and balanced diet during the day, focusing on consistent sleeping habits every night, optimizing recovery and fueling and hydration before, during, and after training, you will be able to stay more consistent with your runs, maintain a body that is strong, fit, fueled and healthy.
Eat Well, Sleep Well, Train Well!