Not for everyone and not always: when intermittent fasting works and when it harms

Intermittent fasting is often presented as a universal recipe for longevity: eat less, live longer. But after the age of 30–40, this approach can work against the body — accelerating muscle loss, impairing recovery, and disrupting hormonal balance, especially with regular physical activity.Why can something that works well at 25 have the opposite effect after 40? Which diets truly have an evidence base for longevity, who is intermittent fasting suitable for and who might it harm, and how can you combine sports and food to slow down aging? LIGA.net I discussed it in detail with Alina Moshenska, an endocrinologist, nutritionist, and sports medicine doctor.The full version includes explanations about RED-S, hormonal risks, muscle loss, and personalized nutrition and training combinations for those over 30–40 years old.Key principle: Nutrition should match training.The basic rule, as emphasized by Alina Moshenska, is that the type of nutrition should correspond to the energy demand and hormonal response of a specific workout. It is the discrepancy between the load and available energy that most often leads to exhaustion, muscle loss, and hormonal imbalances.Strength trainingStrength training is best combined with a balanced diet. with a diet containing sufficient protein: 1.5-2.0 g per kilogram of body weight (in the absence of kidney disease), and don't forget about complex carbohydrates.Read alsoStyle or functionality: equipment rules that will save you from injuries in the gymCarbohydrates support the muscular framework and help lower cortisol levels after a workout. The optimal choice is a Mediterranean-style diet. NutritionAccording to the doctor, a calorie deficit or strict intermittent fasting combined with strength training reduces the anabolic response and can lead to muscle loss, impaired recovery, and the development of delayed onset muscle soreness (DOMS).Interval training and HIITInterval and high-intensity interval training require sufficient energy supply, in particular Nutrition with an emphasis on carbohydrates. Performing such training against the background of energy deficit increases the risk of hormonal disorders in both women and men, in particular the development of the so-called athlete's triad.ReferenceRED-S, or athlete's triad, is a condition that occurs when the body does not receive enough energy for the level of physical activity that is placed on it for a long time. Most often, it is the result of a combination of intense training, restricted eating, and a constant calorie deficit.At the same time, HIIT is not recommended for people with uncompensated anxiety disorders, sleep disorders, deficiency conditions, and clinically pronounced endocrinological pathologies, including manifest thyroid dysfunction.Walking and low-intensity activityWalking or low-intensity activity combines well with intermittent fasting, Mediterranean diet and a moderate calorie deficit within 10-20% of the daily requirement. This combination improves insulin sensitivity without the risk of muscle mass loss.How to Preserve Muscle After 30-40 Years of AgeThe most evidence-based approach to preserving muscle mass after 30-40 years of age includes:sufficient protein (1.5-2.0 g/kg) with an even distribution throughout the day (approximately 25-30 g in 3-4 meals);adequate energy value of the diet without a chronic deficit;Strength training 2-3 times a week.The Mediterranean diet and adequate protein are the best combination for longevity and muscles.At the same time, common mistakes include:prolonged interval feeding without protein compensation;the attitude of "it's not enough for them, because after 40 years it's supposed to be like that";Excessive focus on cardio and fear of carbohydrates, which can lead to increased cortisol and decreased sex hormone levels.HIIT and hormonal balance: who is it suitable for?High-intensity interval training can be beneficial for young or well-trained individuals without sleep disorders, chronic calorie deficits, or deficiency conditions, and provided that adrenal and kidney functions are normal. At the same time, it can be harmful to women with menstrual cycle disorders, people with eating disorders, after infections, including COVID, with anemia, and with uncompensated endocrinological pathologies.A safer option is to perform HIIT not on an empty stomach, with the consumption of complex carbohydrates after training and limiting the frequency to 1-2 times a week.Intermittent fasting: an anti-aging method or not?Time-restricted eating can be beneficial for people with low physical activity, excess body weight, and in the absence of regular intense workouts.At the same time, this approach may be harmful to those who train three or more times a week, women in perimenopause and menopause, and people with iron or protein deficiency.Anti-aging is not about starvation, but about combining metabolic flexibility and muscle mass.Mediterranean Diet and Personalized Combinations for Different GroupsThe Mediterranean diet has the strongest evidence base for longevity due to its emphasis on unsaturated fats, polyphenols, adequate protein, and a pronounced anti-inflammatory effect. It works best in conjunction with regular walking, strength training, and moderate cardio – with a focus on daily activity.For people with sedentary jobs, the optimal approach is a combination of walking and strength training twice a week, protein in every meal, and limiting ultra-processed foods. During perimenopause and menopause, strength training becomes essential, and complex carbohydrates, healthy sleep, recovery, and correction of deficient conditions after checking test results remain important.For insulin resistance, strength training combined with moderate cardio at a heart rate of about 110-130, regular meals, protein and fiber, and avoiding HIIT at the start are recommended.There is no universal "ideal" diet or training, emphasizes Alina Moshenska. There is a correlation between physical activity, hormonal status, and available energy. The key task is to avoid RED-S, the energy deficiency in sports syndrome, which triggers most hormonal disorders.Read alsoElite Longevity Centers and the Anti-Aging Boom: What the Rich Are Paying For

Not for everyone and not always: when intermittent fasting works and when it harms

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