Carbs eaten at night tend to evoke a greater insulin response, fueling the processes that facilitate fat storage and suppress fat burning.
By Brad Schoenfeld, Ph.D.
To a degree, there is some benefit to cutting back on starches before bedtime. The trouble with starchy carbs is that they tend to be more readily transformed to fat when eaten late at night. Here’s why: The primary function of carbohydrates is to supply short-term energy for your daily activities. If carbs are not used immediately for fuel, they have two possible fates: they either are stored as glycogen in your liver and muscles or are indirectly (or in some cases directly) converted into fatty acids and stored in adipose tissue as body fat. Since activity levels usually are lowest during the evening hours, there is a diminished use of carbs for fuel. Hypothetically, this sets up an environment where the body is more inclined to convert carbs into fat.
Compounding matters is the diurnal nature of insulin sensitivity. Studies have shown that insulin sensitivity is highest in the morning. This means your body is better able to assimilate carbs at this time, thereby keeping blood sugar levels stable. As the day wears on, insulin sensitivity gradually diminishes and by evening, it’s at its nadir. Hence, carbs eaten at night tend to evoke a greater insulin response, fueling the processes that facilitate fat storage and suppress fat burning.
What’s more, consuming starches at night has a carry-over effect to the next day. Eating a carbohydrate-rich dinner tends to increase the insulin response of the following morning’s meal. So not only are insulin levels elevated after dinner, but they remain that way through breakfast, too.
Another factor to consider is the effect of carbohydrate on appetite. While protein (and, to a certain degree, fat) helps to suppress hunger, carbs tend to increase it. Through various mechanisms, the breakdown of starches into glucose enhances the urge to eat. This increases the potential to have a late-night snack – one of the biggest culprits in unwanted weight gain.
Ideally, it’s best to consume carbs early in the day, when your activity and insulin levels are at their peak. Breakfast is the time to load up on complex carbs. After an overnight fast, glycogen is depleted from your liver (and, to a lesser extent, your muscles). Since glycogen has important physiologic significance to the onset of starvation, the body strives to replenish these glycogen stores and tends to utilize carbs for this purpose rather than fat storage after you have “broken the fast.” A large bowl of rolled oats or bran cereal with some fruit is ideal. It’ll help to fuel your daily activities and keep you physically and mentally fit throughout the day.
On the other hand, it is best to limit your dinner fare to fibrous, vegetable-based carb sources. Fibrous vegetables tend to be extremely low in total calories and because of their bulk are very filling. For supper, consider eating a meal consisting of lean poultry or fish combined with a large bowl of salad greens. Other vegetables (i.e., broccoli, string beans, cauliflower, zucchini, etc.) also make fine nighttime carbohydrate choices and will reduce the potential for unwanted body fat storage.
Now, understand that cutting out starches at night won’t have dramatic effects on body fat levels. At most, we’re talking 1 or 2 pounds. But if you’re looking to optimize your physique, it can have a subtle but notable effect on your appearance.