Bollywood actor Kartik Aaryan, who recently won the National Film Award for Best Actor for his performance in Chandu Champion, has spoken about the drastic change in his body composition during the making of the film. In an Instagram post, Aaryan said his body fat had gone from 39 percent to 7 percent over the course of one and a half years.

In the post, Aaryan linked the transformation to the life of Paralympic gold medallist Murlikant Petkar, whom he played in the film. He wrote that the journey had made him a stronger person, and added that “if you can dream it, then you can achieve it.”

Aaryan also spoke about changes in his daily routine during this period. He described himself as having gone from being an insomniac to a fitness enthusiast.

What research says about rapid fat loss 

While transformations of this kind are often described as inspiring, research on body composition points to musculoskeletal and hormonal effects that can accompany rapid and extreme changes in body fat.

A 2024 review published in the journal Obesity Reviews titled “Strategies for minimizing muscle loss during use of incretin-mimetic drugs for treatment of obesity,” found that participants in clinical trials lost 10 percent or more of their muscle mass over interventions lasting 68 to 72 weeks. 

The authors noted that this was roughly equivalent to two decades of age-related muscle decline, and said such losses could lead to “reduced functional and metabolic health” and other complications.

A separate 2025 paper by Harvard Medical School, which examined the consequences of lean mass loss during weight reduction, described skeletal muscle as “a critical determinant of ambulation, physical function and metabolic health.” It also pointed to the risks of weight regain and weight cycling when muscle mass is not preserved during a weight loss process.

On the hormonal side, a study published in the journal PLOS ONE in January 2024, analysed data from nearly 6,000 participants in the United States National Health and Nutrition Examination Survey. 

The study found that testosterone levels in men were closely linked to body fat percentage. It noted that a higher percentage of lean mass was associated with higher testosterone levels, while a higher percentage of body fat was linked to lower levels. The authors concluded that their findings “support a negative association between body fat and testosterone levels in males.”

Muscle loss can accompany weight loss, says endocrinologist

Dr Mahesh D M, senior consultant, endocrinology, at Aster CMI Hospital in Bangalore, said Aaryan’s reported reduction in body fat from 39 percent to 7 percent over 18 months would not, by itself, establish that the transformation was harmful. The health risks would depend on how the weight and fat loss was achieved, particularly whether it involved prolonged energy restriction, inadequate nutrition or excessive exercise.

“It is possible to change from a body composition characterised by a high body fat to a very lean one within the 18-month period, provided that it was gradual, nutritional needs were met, and there was proper supervision during the workouts,” he said.

The greater concern, he said, would be “if there is an extremely aggressive or lengthy calorie deficit, especially when combined with rigorous workouts,” as inadequate energy availability can affect hormones, bones, immunity and physical performance.

Dr Mahesh said muscle loss can also accompany substantial weight loss, particularly “when the calorie deficit is high, protein consumption is low, and there is no resistance training.” He said the aim should be “maximising fat loss while retaining muscles” through adequate protein, resistance training and a balanced calorie deficit.

Referring to International Olympic Committee guidance, he noted that excessive pursuit of very low body fat in athletes can be risky because low energy availability may impair muscle function.

He stressed that “the worry lies in whether achieving such a 7 percent body fat percentage involves extreme or excessive energy restriction,” rather than the 7 percent figure itself. Extreme energy deprivation, he said, can disrupt the reproductive hormone axis in men, with symptoms such as fatigue, erectile dysfunction and poor recovery warranting testosterone testing.

For anyone attempting a major body-composition transformation, Dr Mahesh recommended a medical evaluation before starting, including blood pressure checks and, depending on individual history, tests such as CBC, blood glucose, lipids, and liver, kidney and thyroid function. Hormonal disruption is often reversible when identified early, he said, although recovery “does not always happen instantly,” and some effects may not fully resolve.

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