If you’re trying to shed pounds, you may think that eating as little as possible for as long as possible is the best strategy. However, restrictive fasting like this can come at a significant cost to your overall health. While this approach may cause a caloric deficit quickly, its long-term effects on muscle mass, nutrient levels, and even organ health are a good reason to focus on mores sustainable, healthier strategies for weight loss.
To shed some light on the toll that restrictive fasting can take on your body, we spoke to health experts Annie B. Kay, MS, RDN, C-IAYT and registered dietitian Trista Best. They warned against the loss of muscle mass, nutrient deficiencies, and more. Find all of their expert insight and advice below.
Downsides of restrictive fasting
Intermittent fasting—a method with a focus on the time at which you eat, rather than what you're eating—does have potential benefits, including the treatment of diabetes and heart disease. However, putting yourself through highly restrictive fasting, intense calorie cutting, and ignoring hunger cues is a different story.
In addition to the fact that severe restriction can lead to an unhealthy relationship with food, it can have long-term effects on your physical health, including loss of muscle mass. "The downside of fasting is that it can undermine mental health or relationship with food, and create something called sarcopenia—loss of muscle mass, and also possible loss of bone mass," explains Kay.
While fasting might seem like an effective way to lose weight quickly, Kay emphasizes the unintended consequences. "When we restrict calories and protein, it's so easy to lose muscle. It's harder to lose fat—you have to work it differently, often with a higher protein, richer healthful fat, lower carbohydrate way of eating for those in the second half of life."
Another major concern is the lack of essential nutrients. "If a person undergoes prolonged periods of fasting, it can cause long-term damage to their body," warns Best. "It can lead to conditions such as liver and kidney problems, anemia, a weakened immune system, and an irregular heartbeat." Nutrient deficiencies resulting from restrictive fasting can further exacerbate these issues, leading to muscle breakdown and other health complications.
Instead of putting yourself at risk of these downsides, it's best to pursue a balanced approach to weight loss. Incorporating higher protein intake, healthy fats, and moderate carbohydrates can not only aid in fat loss but also support overall health.
So, remember: While restrictive fasting may promise quick results, the risks aren't worth it. In 2025, focus on keeping your body happy and healthy by providing it with the nutrients it needs.
