Intermittent fasting has become one of the most popular dietary approaches in recent years, touted for its benefits in weight loss, metabolic health, and disease prevention. However, misconceptions and myths about intermittent fasting continue to persist, sowing confusion and discouraging people from trying this effective lifestyle intervention.

In a recent review published in Nature Reviews Endocrinology, a team of leading nutrition researchers methodically examined some of the most common myths about intermittent fasting and provided the scientific evidence to debunk them. As intermittent fasting continues to grow in popularity, it’s important to separate fact from fiction and empower people to make informed decisions about incorporating fasting into their health regimen.

Myth 1: Intermittent Fasting Harms Sex Hormones

One of the most persistent myths about intermittent fasting is that it can have deleterious effects on sex hormones, particularly in women. The concern is that the fasting periods could disrupt the delicate balance of estrogen, testosterone, and other reproductive hormones, leading to menstrual irregularities, fertility issues, and loss of libido.

However, the research tells a different story. Studies have consistently shown that in both women and men, intermittent fasting does not significantly impact sex hormone levels. In women, levels of estrogen, testosterone, sex hormone binding globulin (SHBG), and other reproductive hormones remain stable during intermittent fasting protocols lasting up to 1 year. Similarly, in men with obesity, testosterone and SHBG concentrations do not change with intermittent fasting.

The one exception appears to be in women with polycystic ovary syndrome (PCOS), a hormonal condition characterized by elevated androgen levels. Emerging evidence suggests that intermittent fasting may actually help regulate hyperandrogenism in this population. After 1-3 months of time-restricted eating, women with PCOS have shown reductions in testosterone and increases in SHBG, leading to improvements in the free androgen index, a key marker of androgen excess.

These findings indicate that intermittent fasting does not disrupt sex hormones in healthy individuals, and may even offer benefits for women with certain hormonal imbalances. As with any dietary intervention, those with a history of eating disorders or other medical conditions should consult their healthcare provider before embarking on an intermittent fasting regimen.

Myth 2: Intermittent Fasting Causes Excessive Muscle Loss

Another common misconception is that intermittent fasting leads to excessive loss of lean muscle mass, more so than other weight loss approaches. The concern is that the periods of fasting could accelerate the breakdown of muscle protein stores, compromising strength and physical function.

However, the research tells a different story. When comparing the body composition changes between intermittent fasting and continuous calorie restriction, the two approaches show remarkably similar results. Approximately 75% of the total weight loss comes from fat mass, while the remaining 25% is from lean muscle mass. There is no evidence that intermittent fasting causes augmented protein turnover or greater lean mass loss compared to other weight loss diets.

In fact, strategies to preserve muscle mass during intermittent fasting are well-established. By combining intermittent fasting with resistance training and increasing dietary protein intake, individuals can effectively retain muscle mass even during periods of calorie restriction and weight loss. These muscle-preserving strategies are not unique to intermittent fasting, as similar findings have been observed with continuous calorie restriction protocols as well.

Importantly, these muscle-sparing effects of intermittent fasting have also been observed in older adults, a population particularly vulnerable to age-related muscle loss (sarcopenia). While the research is still limited in this area, current evidence suggests that time-restricted eating does not lead to detrimental reductions in skeletal muscle mass in older individuals. Further research is needed to determine the optimal protein intake required to prevent sarcopenia in older adults who adopt intermittent fasting.

Myth 3: Intermittent Fasting Decreases Diet Quality

Another common concern is that the restricted eating windows of intermittent fasting could lead to poor dietary choices and decreased diet quality. The worry is that people might compensate for the fasting periods by bingeing on energy-dense, nutrient-poor foods, or that they may increase their intake of stimulants like caffeine to boost energy levels.

However, the research paints a different picture. Studies have consistently shown that key markers of diet quality, such as intake of sugar, saturated fat, cholesterol, fiber, sodium, and caffeine, do not change in individuals following time-restricted eating protocols compared to control groups. Additionally, the proportion of calories from macronutrients (protein, carbohydrates, and fat) remains stable across different intermittent fasting regimens.

The only dietary metric that does change during intermittent fasting is total energy intake. Individuals following time-restricted eating patterns tend to reduce their daily calorie intake by 200-550 calories compared to control groups. These unintentional calorie reductions are the primary driver of the weight loss observed with intermittent fasting, rather than any dramatic shifts in food choices or nutrient intake.

In other words, people don’t seem to drastically alter the types of foods they eat during intermittent fasting – they simply eat less of them. This highlights the power of intermittent fasting as a tool for calorie control and weight management, without the need for overly restrictive or complicated dietary rules.

Myth 4: Intermittent Fasting Leads to Eating Disorders

One of the most understandable concerns about intermittent fasting is its potential to exacerbate disordered eating behaviors, particularly in vulnerable populations like adolescents. The cyclical nature of fasting and feeding periods could conceivably trigger unhealthy preoccupations with food, body image issues, and compulsive eating patterns.

However, the evidence suggests that intermittent fasting, when implemented responsibly, does not increase the risk of eating disorders. In fact, studies have shown that healthy adults following intermittent fasting protocols report fewer food cravings, weight concerns, mood disturbances, and binge-eating behaviors compared to control groups.

That said, it’s crucial to exercise caution when considering intermittent fasting, especially in younger populations. The onset of eating disorders typically occurs between the ages of 12 and 25, and the risk is heightened in adolescents with obesity. For this reason, healthcare providers should closely monitor for any signs of disordered eating behaviors if prescribing intermittent fasting to young patients, and be prepared to immediately discontinue the intervention if any issues arise.

Overall, the scientific evidence paints a very different picture than the persistent myths surrounding intermittent fasting. Far from being a dangerous or extreme dietary approach, intermittent fasting appears to be a safe and effective lifestyle intervention for weight management and metabolic health, with a similar safety profile to other popular diets like low-carb or Mediterranean.

Of course, as with any dietary change, individuals should consult their healthcare provider, especially if they have a history of eating disorders or other medical conditions. But for the vast majority of people, intermittent fasting can be a useful tool in the pursuit of better health, without the need to fear the many unfounded myths that continue to circulate.

By separating fact from fiction, we can empower people to make informed decisions about incorporating intermittent fasting into their lives, and reap the benefits of this evidence-based approach to better health.