However, it’s important to be careful when using running to lose weight. This is because it’s best to lose weight gradually and sustainably in order not to have a negative impact on your health or running performance.

If you’re using running as part of your weight loss strategy, remember that reducing your food intake isn’t the only way to lower calories—running burns calories, too. If you’re actively increasing the amount of running you’re doing, you may not want to adjust your food intake at all. Additionally, you’ll want to think not just about how much you eat, but what you eat. We’ll explore this in more detail in this article.

Photo Weight scales with measuring tape

When Is the Best Time to Lose Weight?

Runners who are competing in races, whether recreational or elite, should take their race season into account when thinking about a weight loss plan. While it might be tempting to try to get into your best shape by losing a few kilos, race season isn’t the time to do this.

Maintaining a calorie deficit while simultaneously meeting the demands of training is likely to compromise recovery, training adaptation, and your performance. Low energy availability is also a serious nutritional concern for runners, and this can cause physical health concerns, like impaired immunity, hormonal imbalances, and low bone density.

If you would like to lose body fat in preparation for race season, the off-season is the best time to do it. Your body is better able to handle a lower calorie intake when your training load is lower.

Losing Weight Safely

To lose weight safely while running, aim to do so gradually. In athletes, a body mass loss of around 0.5–1% of bodyweight per week is considered a healthy amount that preserves lean muscle mass, which is crucial to your performance. Losing weight faster can cause muscle loss alongside fat, which is counterproductive for athletic performance.

For a 70 kg athlete, that means a maximum of roughly 0.5–0.7 kg per week. In practice, a daily energy deficit of around 250–500 kcal is a reasonable target for most runners. Avoid dropping below approximately 1,500 kcal per day, as intakes below this level in active individuals are associated with muscle loss, increased injury risk, and a higher likelihood of disordered eating patterns.

To put this in perspective, 1 lb of fat contains approximately 3,500 calories (this is not an exact science because your body is brilliant at regulating itself, but it’s a rough starting point). Combining a modest daily calorie deficit with running can help you stay in a reasonable calorie deficit, and over time, this can lead to consistent, gradual weight loss.

Protein intake becomes particularly important when losing weight. Eating enough protein actually helps you maintain your muscle mass while you’re in a calorie deficit, making it particularly important. It also supports recovery from workouts and helps keep you feeling fuller for longer.

Aim for the higher end of protein recommendations, or around 1.6–2.4 g of protein per kilogram of bodyweight daily. In practice, for a 70 kg runner, this looks like 112–168 g. Spreading this across three to four meals, each containing 20–40 g of protein, can help you reach your protein goal. It’s important to continue to eat enough carbs at meals, especially those before and after training.

If you eat too little, you leave yourself susceptible to injury and illness, both of which will set your plans back. Pay attention to your energy levels, and temporarily track your food intake if you’d like to. A 250–500 kcal deficit per day is a reasonable target, and remember, your calorie expenditure from running also needs to be accounted for.

Photo Healthy vegetable based meal

Practical Portion Size Guidance

Rather than counting calories precisely, a practical approach is to use your hand as a guide:

• Protein (meat, fish, eggs, pulses): A palm-sized portion is roughly one serving.
• Carbohydrates (rice, pasta, potatoes, oats): A cupped-hand portion is one serving, though many runners need more than this.
• Vegetables: Try to fill around one-third to one-half of your plate.
• Fats (oils, nuts, avocado): A thumb-sized portion is about one serving.

These are starting points, not rigid rules. It’s important to remember that carbohydrates shouldn’t be restricted, especially around training. Athletes with higher training loads will need more, particularly carbohydrates around sessions.

A useful strategy to reduce your calorie intake is to eat more satisfying and filling meals. Fruits and vegetables, while containing health-promoting micronutrients, are also rich in fibre and water, which can help keep you feeling fuller for longer. Whole grains like brown pasta, oats, and quinoa are also good sources of fibre. And while you may not want to have them before a run, beans and lentils are a good source of fibre and protein, and adding them to a meal can help you feel more satisfied and less likely to reach for extra snacks.

If you’re planning a significant change to your body composition or have had challenges with weight loss, it’s a good idea to work with a registered dietitian or nutritionist who has experience working with athletes. They can help you set realistic targets and monitor for signs of under-fuelling.

References

Aragon, A. A., et al. (2017). International society of sports nutrition position stand: diets and body composition. Journal of the International Society of Sports Nutrition, 14, 16. https://doi.org/10.1186/s12970-017-0174-y

Garthe, I., et al. (2011). Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International journal of sport nutrition and exercise metabolism, 21(2), 97–104. https://doi.org/10.1123/ijsnem.21.2.97

Hector, A. & Phillips, S. (2018). Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance. International journal of sport nutrition and exercise metabolism, 28(2). https://journals.humankinetics.com/view/journals/ijsnem/28/2/article-p170.xml

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