Is it good to exercise if you are underweight?

Running with underweight

A low body weight in running means fast times in competition. At least that is how it looks at first glance. And that may be true at the top of the world. However, if you look at the starting line at fun runs, you will see both male and female participants, where you first say "Why is he so far ahead ?!" thinks and can't even see him from a distance after the third corner. What counts in terms of performance and health is not only the number that is on the scales and shows the body weight, but above all the overall constitution of the athlete. With these thoughts in mind, one should therefore also consider the subject of "underweight" and the informative value of the underlying body mass index (BMI).

What does underweight mean?

Anyone who has a BMI of less than 18.5 is considered underweight. However, underweight, as evidenced by figures such as the BMI, does not necessarily mean physical problems, especially for runners. Nevertheless, underweight people are considered to be a risk group in terms of their health, as well as overweight athletes.

What is the body mass index and what is its significance?

First of all: The BMI is only an orientation aid, which is only of limited informative value, especially for endurance and top athletes. The BMI is calculated from the body weight in kilograms divided by the height in meters squared. If you calculate your BMI, the result is a number between 17 and 39. The BMI does not take into account differences in body composition such as fat, muscle tissue and water percentage.

The World Health Organization (WHO) has created a table for men and women to give an orientation of the BMI.

Classification of the BMI for women

under 17.49 = underweight

17.5 to 23.99 = normal weight

24 - 26.49 = overweight level 1

26.5 - 28.99 = overweight level 2

29 - 31.49 = Obesity grade 1, level 1

31.5 to 33.99 = grade 1 obesity, grade 2

34 to 36.49 = Grade 2 Obesity, Level 1

36.5 to 38.99 = Grade 2 Obesity, Level 2

over 39 = obesity grade 3

Classification of the BMI in men

under 18.49 = underweight

18.5 to 24.99 = normal weight

25 to 27.49 = overweight level 1

27.5 to 29.99 = overweight level 2

30 to 32.49 = Grade 1 Obesity, Level 1

32.5 to 34.99 = grade 1 obesity, grade 2

35 to 37.49 = Grade 2 Obesity, Level 1

37.5 to 39.99 = Grade 2 obesity, Level 2

over 40 = obesity grade 3

The BMI is not always meaningful

There are many groups of people for whom the calculation of the BMI is possible, but not useful or meaningful. Basically, there are already differences between individual countries: Ethiopians and Chinese have, on average, a lower BMI than people who live in Germany, regardless of their sporting activity. These in turn have a lower BMI than African Americans. There are also differences between particularly small and particularly large people: In comparison, small people have a higher BMI than very tall people. After all, the organ mass remains almost the same. And anyone who is active in weight training has significantly more muscle mass than an endurance athlete at the same level of performance. After calculating the BMI, however, it would turn out that the strength athlete is overweight and the endurance athlete is underweight. For both athletes, the calculation of the BMI would accordingly have no informative value.

If the BMI is low, go to the check-up before starting training

"If you are underweight, you should undergo a full medical examination before starting regular running," recommends health expert Dr. med. Roger Hofmann. The goal of visiting the doctor is to rule out serious illnesses that lead to permanent weight loss. It is therefore important whether you have always been very slim (genetic) or have only recently lost weight. A detailed examination also includes a clinical examination of the whole body status, in particular of the musculoskeletal system and cardiovascular system (preferably including stress ergometry) as well as a complete blood count in order to be able to identify and treat possible deficiency symptoms. In connection with low body weight, the gastrointestinal tract and the thyroid gland should also be examined (stool, laboratory and ultrasound examination). For women, a supplementary gynecological clarification is useful. After about 12 weeks of continuous training units, performance diagnostics will help determine future training areas and make training more efficient so that you can achieve your goals more quickly.

Read here the most important things about the check-up before starting the run

Underweight and running training are not mutually exclusive

As long as all results are inconspicuous, nothing stands in the way of running. A critical, professional and objective assessment of eating habits can help avoid further unwanted weight loss due to the increasing exercise-related calorie consumption.

Check your body weight regularly and record the development, ideally in combination with your training kilometers, so that you can recognize further weight loss early on and then - after consulting your doctor - quickly take countermeasures. Under these conditions, the following also applies in your case: running is healthy!

Complete nutrition against deficiency symptoms and weight loss

Make sure you have a sufficient intake of fat, protein and carbohydrates in accordance with your consumption. With plenty of fluids, fruit and vegetables, you cover your vitamin, trace element and micronutrient requirements. Make sure that vegetables, fruits, fish and meat are of high quality by buying little processed and regional products without additives.

If your blood count shows a deficiency in individual trace elements or minerals, you should treat this with dietary supplements in consultation with your doctor. Then it makes sense to have a check-up at regular intervals of three to six months after starting the run.

All information about iron deficiency in endurance sports

Conclusion: running is also possible with underweight!

If you have checked yourself thoroughly with the doctor beforehand and make sure that you eat enough and wholesome foods, running and being underweight are not mutually exclusive. Always consider your body weight in relation to your training kilometers and take action as soon as your weight changes significantly.

One more sentence should generally be said about running with underweight: Anyone who starts running despite being underweight because of running, is doing well within the healthy range. However, anyone who runs despite being underweight in order to keep underweight or to continue to lose weight should definitely seek medical advice, keyword "anorexia", "sports addiction" and "anorexia nervosa".

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