Most Singaporeans have indulged in supper or midnight snacking at some point in their lives. It might have been after a midnight movie or a late night party, or because of hunger pangs while studying late through the night. Similarly, most of us have heard the advice that we should not sleep on a “full stomach”, and that late meals are bad for health. Is this true or merely an old wives’ tale? Let’s look at the studies and evidence present in the medical literature.

Researchers in Mexico who conducted tests on rats found that constant eating during their rest period is associated with higher levels of fat called triglycerides. As we all know, high blood fat levels are associated with an increased risk of diabetes and heart disease. Hence, the researchers cautioned that people who eat regularly at night, such as night shift workers, may be at increased risk of cardiovascular diseases, although the occasional bed-time snack or late dinner is unlikely to cause lasting damage.

…people who eat regularly at night, such as night shift workers, may be at increased risk of cardiovascular diseases, although the occasional bed-time snack or late dinner is unlikely to cause lasting damage.

In humans, some studies demonstrate a link between eating night time snacks and poor health outcomes such as obesity, increased cholesterol, increased blood sugar levels, and increased risk of coronary heart disease. There are several explanations for these observations. First, eating late at night results in reduced fat and carbohydrate metabolism (or breakdown) by the body. Second, there is reduced energy expenditure for night eaters. This may be due to fewer opportunities to burn off calories at night, and hence they tend to put on weight more easily. Third, eating late into the night means reduced hours of sleep, and this increases the “hunger hormones” (ghrelin) and reduces the “satiety/ fullness hormones” (leptin), resulting in overeating and weight gain. Insufficient sleep can also reduce the body’s sensitivity to the hormone insulin and increase inflammation of blood vessels, hence predisposing a person to diabetes and heart problems.

Human trials on night shift workers concur with the above result and show a higher prevalence of overweightness, abdominal obesity, elevated triglycerides, abnormal lipid levels, pre-diabetes, and decreased kidney function, when compared to day-time workers.

Most recently, a study presented at the American Heart Association’s Scientific Sessions in November 2019 reported that participants who consumed more calories after 6pm tended to have poorer cardiovascular health. In particular, every 1% increase in calories consumed in the evening increased the likelihood of higher blood pressure, blood sugar and body mass index (BMI). These negative health effects are all risk factors for heart problems and stroke.

In summary, we need to be mindful of not just what we eat, but when we eat our food. We should maintain a healthy eating habit by eating a balanced diet (consisting of whole grains, meat, healthy oils, fruit and vegetables) and avoiding irregular eating patterns, such as skipping meals and late night snacking. If you do wake up in the middle of the night and feel the urge to eat, ideally you should try to go back to sleep without eating anything. However, if you feel hungry and must eat, you should choose a high fiber snack or a glass of milk. Snacks with high sugar and fat content should be avoided. Also to avoid late-night cravings in the first place, you should take small frequent meals throughout the day and never skip breakfast.

References:

[1] St-Onge et al. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation 2017;135(9):e96-e121. [2] Moran-Ramos et al. The suprachiasmatic nucleus drives day-night variations in postprandial triglyceride uptake into skeletal muscle and brown adipose tissue. Experimental Physiology 2017;10:1113. [3] Kinsey et al. The Health Impact of Nighttime Eating: Old and New Perspectives. Nutrients 2015;7(4):2648-2662