The belief that consuming carbohydrates after a certain time, like 6 or 7 pm, leads to increased fat storage is a pervasive myth. This misconception stems from two primary lines of reasoning, both of which lack scientific support.
The first theory posits that metabolism slows down during sleep, making the body more likely to store carbs as fat rather than burn them for energy. However, this misunderstands the concept of metabolism. Metabolic rate, which determines total daily energy expenditure (TDEE), comprises resting metabolic rate (RMR), exercise activity thermogenesis (EAT), non-exercise activity thermogenesis (NEAT), and the thermic effect of food. During sleep, EAT, NEAT, and the thermic effect of food are negligible, leaving RMR as the primary component. Studies have shown that RMR during sleep is virtually identical to RMR while awake and resting. Therefore, consuming carbs at night is metabolically no different than eating them during the day and remaining at rest.
Furthermore, even if metabolic rate were lower at night, transient changes in metabolic rate don’t dictate body composition. Long-term net caloric deficit over 24 hours or longer determines fat loss or gain. Even if carbs consumed at night were initially stored as fat due to a temporarily lower metabolic rate, that energy would eventually be utilized if a net caloric deficit is maintained.
Finally, dietary carbohydrates are not easily converted to body fat. The process, known as de novo lipogenesis, is rare in humans under normal dietary conditions. Instead, consuming carbs primarily suppresses fat oxidation, leading to increased storage of dietary fat, while the carbs are more likely used for muscle or liver glycogen replenishment or burned as fuel.
The second theory suggests that insulin sensitivity is lower in the evening, hindering the body’s ability to process carbohydrates effectively. While some studies show a lower insulin response to an evening meal compared to a morning meal, this is likely due to the overnight fast, which is known to improve insulin sensitivity. When comparing meals consumed without a preceding fast, insulin sensitivity remains consistent throughout the day. Thus, insulin sensitivity isn’t inherently worse in the evening; it simply peaks after the overnight fast and then remains relatively stable. Focusing on long-term improvements in insulin sensitivity through maintaining a healthy body composition, regular exercise, and a balanced diet is more impactful than worrying about transient daily fluctuations.
A 2017 systematic review and meta-analysis by Fong et al. examined the relationship between evening meal size and weight loss. While some individual studies showed that smaller evening meals led to greater weight loss, the overall effect was not statistically significant when the results were pooled. The authors concluded that there’s insufficient evidence to support the notion that smaller dinners are beneficial for weight management.
Ultimately, the idea that limiting carbs at night due to metabolic or insulin sensitivity concerns is a myth. Instead, prioritize an eating pattern that aligns with your individual schedule, preferences, and appetite fluctuations. Some individuals experience increased appetite in the evening, and in such cases, there’s no harm in consuming more calories, including carbs, later in the day, as long as it fits within their overall caloric goals. Conversely, if late-night snacking is a challenge, setting a cut-off time for eating might be a helpful strategy. Focus on establishing sustainable and enjoyable eating habits that support your overall health and fitness goals, rather than adhering to unsubstantiated dietary restrictions.
