How Not to Lose Muscle Mass During Weight Loss?

Many people succumb to the illusion that a slim figure always means good health. Meanwhile, despite normal BMI values, it is possible to suffer from the so-called “hidden obesity”, with a skinny fat figure characterised by too much body fat in relation to muscles. It is often the result of an ill-advised weight loss diet. Find out how to prevent it.

26 November 2024

What is skinny fat figure?

The skinny fat figure, otherwise known as “normal weight obesity”, is a condition in which a person’s body weight is low or normal, but body proportions indicate an excess of body fat relative to muscle mass. A person with such a figure may appear slim and weigh not much, but their body does not function optimally and their health may leave much to be desired. Too high a percentage of body fat, characteristic of a skinny fat figure, can be associated with:

greater risk of metabolic diseases as well as risk of type 2 diabetes, hyperinsulinemia, insulin resistance, elevated cholesterol, hypertension,
greater risk of occurence of cardiovascular diseases,
greater risk of back and postural problems,
greater risk of disability,
shorter life expectancy.

“Skinny fat” is a colloquial term, but the problem is serious. In scientific language, this condition is referred to as “metabolically obese normal weight” (MONW). The term describes people whose body weight and BMI are within normal, but who are at risk of metabolic complications typical of overweight and obesity. The phenomenon was first described in 1981, when researchers noted that in normal-weight people, type 2 diabetes, hypertension, elevated triglycerides and hyperinsulinemia could co-occur. An association of these disorders with low muscle mass was also observed.

How to diagnose skinny fat figure?

There are no uniform diagnostic criteria for the skinny fat figure. For its semi-professional diagnosis, however, the following are used:

body composition analysis and calculation of body fat percentage. An alarming result is above 20% body fat in men and above 30% body fat in women;
assessment of various components of the metabolic syndrome (blood pressure, HDL cholesterol, glucose levels). Abnormal results may indicate metabolic complications resulting from high body fat;
calculation of the HOMA-IR index (to confirm insulin resistance).

The BMI index, which only takes into account body weight and height, is not sufficient to diagnose a skinny fat figure. So how to independently assess whether this problem may also apply to you? The best solution is to perform a body composition analysis to determine the percentage of body fat. You can measure body fat using:

body fat caliper – preferably with an experienced dietitian with the right equipment, who will immediately analyse the result;
bioelectrical impedance analysis (BIA) – using body composition analysers. This is the most popular and accessible method of body composition analysis, available at most fitness clubs and gyms;
hydrostatic weighing – it is a method involving weighing in water. It is very accurate, but requires specialised equipment and is less available;
DEXA (Dual-Energy X-Ray Absorptiometry) – this is an advanced method that uses X-rays to accurately measure fat, muscle and bone tissue. However, it is expensive, available mainly in medical facilities and used mostly in clinical trials;
3D scanning – creating a three-dimensional model of the body to assess body composition.

It is assumed that the normal level of body fat in women is about 20-30%, and in men about 10-20%. Individuals with a skinny fat figure may therefore have a body fat content of >20% for men and >30% for women. At the same time, to not meet the criterion of being overweight, the BMI must be lower than 25.

Often, an additional symptom of a skinny fat figure is the accumulation of fat around the abdomen and waist, as well as cellulite. Due to the lack of clear criteria for officially diagnosing MONW, there is also no accurate data on its frequency. According to estimates from the National Health and Nutrition Examination Surveys, the problem can affect up to 25% of adults with “normal” body weight.

How is skinny fat figure formed? 7 reasons

Skinny fat syndrome can have various causes. Most often it is due to dietary mistakes, bad habits and lack of physical activity. Here are some elements that can lead to a skinny fat figure.

Improperly conducted weight loss diet. Losing weight too fast and drastically reducing the calorie content of the diet below Basal Metabolic Rate (BMR) leads to loss of muscle mass. As a result, you actually manage to see a lower score on the scales, but it is not lost body fat, but valuable muscle tissue.
Failure to analyse body composition before starting a weight loss diet and relying only on BMI. This indicator does not reflect the ratio between muscles and body fat. BMI does not show what condition your body is in, despite the fact that it is the most commonly used indicator to assess overweight and obesity. If you focus only on body weight on a weight loss diet, you may perpetuate behaviours that steer you toward a skinny fat figure.
Insufficient supply of protein in the diet, which is essential for protecting and building muscle mass. If you are in an energy deficit and do not provide enough protein from food, there is a high risk that the body will “take protein” by breaking down muscles.

Lack of physical activity, especially strength training, which plays a key role in maintaining and building muscle mass. While weight loss is possible without exercise, only through an energy deficit – this is not optimal. Without adequate muscle mass, your body will not function effectively.
A processed diet, rich in pro-inflammatory ingredients, simple sugars and saturated fats, while poor in real nutritional macro- and micro-nutrients such as fibre and protein. Such diet promotes the accumulation of fat – especially so-called visceral fat – in the abdomen.
Smoking. Smoking can lead to a decrease in muscle mass and limits the body’s ability to build muscles because it interferes with blood flow and nutrient delivery to tissues.
Alcohol. It is calorific and promotes fat accumulation. In addition, alcohol abuse can cause muscle catabolism (muscle breakdown) and many hormonal problems, such as reduced testosterone levels and elevated cortisol levels. This does not benefit muscle tissue.

It is also possible to have a skinny fat figure without radical weight loss or change in diet. This usually applies to people who are not very physically active, shying away from exercise and sports.

How to prevent a skinny fat figure?

Below you will find some practical tips that can help you avoid the formation of this type of figure or effectively combat it, minimising the risk of associated complications.

Conduct a slow weight loss

When conducting weight loss, never go below BMR (basal metabolic rate) in calorie content. Use a balanced and gradual approach to weight loss, assuming a maximum loss of 0.5 kg of body fat per week. A calorie deficit of 400-600 kcal will therefore be optimal. Don’t be tempted to cut down on calories too much. Drastic calorie deficits not only lead to loss of muscle mass, but can upset hormonal balance, or slow down metabolism.

Avoid detoxes

The most effective long-term way to lose excess body weight is to work on eating habits and a balanced diet. “Miracle diets”, starvation and dietary detoxes will not work in the long term, and often lead to loss of muscle mass. Even intermittent use of such dietary practices is a straight path to a skinny fat figure.

Monitor body composition, not just weight

Body weight should not be the most important measure of success in weight loss or the process of changing eating habits. It is natural that muscles weigh more than fat tissue (comparing the same volume). You can lose kilograms, but not at all get rid of body fat, only the desired muscles. In the long term, a much better measure of progress may be regular body composition analysis or classic circumference measurements. Weighing yourself may be one method used, but don’t consider weight as the best indicator of progress.

Ensure protein in your diet

An adequate supply of protein is crucial both in a healthy balanced daily diet, in a weight loss diet, as well as in the diet of an athlete. It is recommended to consume about 1.5-2 g of protein per kilogram of body weight. Protein is a macronutrient essential for post-exercise recovery and a muscle builder. Consuming high-quality protein in the right amounts helps maintain muscle mass even during a calorie deficit.

Protein has an important function in regulating metabolism, as it is a thermogenic. Its digestion and absorption requires more energy compared to carbohydrates or fats, which increases the body’s energy expenditure. In addition, protein affects the feeling of satiety, which is especially important during weight loss, when appetite control is crucial.

Following a diet rich in protein is the most important dietary recommendation for a skinny fat figure. Make sure you consume a minimum of 25 g of protein in each main meal. In protein meals use:

dairy,
meat,
legumes,
tofu,
fish,
eggs,
protein supplements.

Bet on strength training

Even with an adequate supply of protein, muscle building will not be possible without physical activity. With a skinny fat figure, it is best to bet on properly selected strength training. Strength exercises stimulate synthesis of muscle proteins, which allows you to maintain them during weight loss, or even build them (this is the process of body recomposition, which can be effective especially in beginners). Training activity is therefore not optional, but essential for building muscles.

^References:

^{Pastusiak K. i wsp., Otyłość metaboliczna z prawidłową masą ciała – kontrowersje w diagnostyce, Varia Medica, 2018 tom 2, nr 3, strony 187–191, 2018 Via Medica ISSN 2544-4212.}
^{Ding C., Chan Z., Magkos F., Lean but not healthy: the 'metabolically obese, normal-weight' phenotype, Curr Opin Clin Nutr Metab Care, 2016 Nov, 19(6):408-417, doi: 10.1097/MCO.0000000000000317, PMID: 27552473.}
^{Kapoor N., Thin Fat Obesity: The Tropical Phenotype of Obesity, 2021 Mar 14, In: Feingold K. R., Anawalt B., Blackman M. R., Boyce A., Chrousos G., Corpas E., de Herder W. W., Dhatariya K., Dungan K., Hofland J., Kalra S., Kaltsas G., Kapoor N., Koch C., Kopp P., Korbonits M., Kovacs C. S., Kuohung W., Laferrere B., Levy M., McGee E. A., McLachlan R., New M., Purnell J., Sahay R., Shah A. S., Singer F., Sperling M. A., Stratakis C. A., Trence D. L., Wilson D. P., editors, Endotext [Internet], South Dartmouth (MA): MDText.com, Inc., 2000-, PMID: 33734655.}