How does timing of your last meal affect overnight glucose & metabolic health?

That old advice to stop eating a few hours before bedtime exists for a good reason: Late-night noshing may disrupt your sleep, contribute to weight gain, and increase the risk of metabolic syndrome and Type 2 diabetes.

But sometimes life gets in the way, and suddenly it’s 9 pm, and you’re left wondering if you should eat now or just go to bed and risk a night of hunger-induced insomnia. Understanding the science behind what a late dinner does to your body may help answer this question.

Below, learn about the consequences of late-night eating and what to do if you can’t dine on time.

What is late-night eating?

There’s no official consensus on what time constitutes late-night eating or when the adverse effects associated with it are more likely to kick in (and, as explained below, it may vary by person). Some research has demonstrated that eating a final meal by 6 pm instead of 10 pm is better for maintaining balanced blood sugar and other markers of metabolic health. But different studies use different cut off times; generally, later is worse.

When you eat at night, you’re more likely to experience impaired insulin sensitivity and bigger blood sugar spikes, and preliminary research suggests that higher levels of the circadian-rhythm-regulating hormone melatonin are one reason for this. Melatonin levels begin to rise soon after the sun sets, and they peak between 2 am and 4 am. So, theoretically, the later you eat after the sun goes down, the greater your potential risk of experiencing a blood sugar spike.

But because our schedules can vary so widely, naming a specific cutoff time isn’t practical—instead, a good rule of thumb cited by several experts, including Sara Gottfried, MD, Levels advisor and author of Women, Food, and Hormones, is to stop eating about three hours before bed—and you can consider anything consumed after that “late-night eating.”

A three-hour window helps you avoid bedtime hunger (which could mess with sleep and, in turn, metabolic health) but allows time for digestion, so you’re less likely to get a bout of acid reflux when you hit the sheets. “It also increases the chances that you’ll be able to get in a walk [after dinner] or some other type of gentle physical activity that can help with blood sugar regulation and have beneficial impacts on metabolism,” says registered dietitian Zoë Atlas, MPH, RD.

What happens when you eat a late dinner?

When you eat late at night, and even when you simply stay up too late, you’re acting in a way that’s counter to your body’s natural circadian rhythms. After all, humans are biologically programmed to eat food, be active, and burn fuel during the light, daytime hours, and sleep at night when it’s dark. Experts speculate that the “circadian misalignment” caused by late-night eating is behind some of the metabolic consequences associated with eating more of your calories at night versus earlier in the day, including alterations in insulin sensitivity, levels of hunger and satiety hormones, and the ability to metabolize fats efficiently.

Here are some of the specific metabolic consequences of late-night eating from recent studies.

Bigger blood sugar spikes: Even when your diet remains consistent day to day, its impact on blood glucose may change depending on when you eat most of your food. In a small 2023 crossover study on eight healthy men published in The Journal of Nutrition, a later eating schedule with all meals between 12 pm and 11 pm was associated with, on average, 8-point higher 24-hour mean glucose levels compared to eating an equivalent diet between 8:30 am and 7:30 pm. Similarly, a small 2020 crossover study on 20 healthy men and women, published in The Journal of Clinical Endocrinology & Metabolism, found that eating dinner at 10 pm was associated with an 18% higher blood sugar spike compared to eating the same dinner at 6 pm.

This makes sense, as various studies have shown that insulin secretion and insulin sensitivity, both of which are key for shuttling glucose from the bloodstream into cells, where it can be used for energy, are significantly greater in the morning and decrease in the evening. While the exact mechanisms are not fully understood, the circadian rhythms of melatonin secretion and insulin sensitivity appear to be connected—studies suggest that insulin secretion decreases as melatonin increases, potentially due to melatonin’s inhibitory effect on insulin.

Altered fat metabolism: Eating later also appears to make you break down fatty acids less efficiently. The 2020 study mentioned above found that people eating dinner at 10 pm metabolized fats from their late-night meals about 10% slower. The implication: Per the study’s authors, eating a late meal triggers an anabolic state during sleep that favors the storage of fats over their mobilization and oxidation, which, over time, may contribute to weight gain (as has been demonstrated in animals). The study also noted a prolonged triglyceride peak with the late-night meal, meaning triglycerides remained elevated in the bloodstream for a longer period. A 2023 study found that post-meal triglyceride levels were a stronger predictor of cardiovascular disease than fasting triglycerides, and a separate 2021 study in The American Journal of Clinical Nutrition on 3,362 men and women found that late-night eaters had higher overall triglyceride levels, a known cardiovascular risk factor, along with higher BMI and lower insulin sensitivity on average.

Lower post-meal metabolic rate: Research also suggests that post-meal energy expenditure is lower when you eat later. One small study in the journal Obesity on 13 men and women showed a 44% reduction in diet-induced thermogenesis (i.e., the increase in metabolic rate that follows eating) after an evening meal versus a morning meal, which translates to fewer calories burned at rest.

Greater hunger, despite similar intake: In a small 2022 crossover study in Cell Metabolism, 16 adults who were overweight or obese spent four days following an early eating schedule and four days following a late eating schedule (in which meal times were delayed by 250 minutes compared to the early eating schedule), with a reset period in which participants followed their usual eating habits between the two. Participants were significantly hungrier at various points throughout the day on the later eating schedule despite eating the same foods and performing the same amount of physical activity.

One potential reason: Lab results showed that when their eating was shifted later, they had lower levels of the satiety hormone leptin over the next 24 hours. Eating later was also associated with decreased energy expenditure and increased expression of genes that promote fat storage.

Difficulty losing weight: All of these metabolic consequences could, over time, translate to greater difficulty losing weight as well. In a 2022 meta-analysis of nine clinical trials (each ranging from 8 to 193 participants) published in Obesity Reviews, people assigned to follow calorie-restricted diets tended to lose more weight if they ate a larger proportion of their calories earlier in the day compared to those who ate a comparatively higher proportion of their calories later in the day. Late eaters also experienced less improvement in fasting blood sugar, insulin resistance, and LDL cholesterol compared to early eaters following energy-restricted diets.

Interestingly, some research suggests that late-night eating may not be equally detrimental for everyone. It may partly depend on your chronotype—that is, whether you are naturally a morning person or a night owl.

• In the 2020 study, participants whose typical bedtime was between 2 am and 3 am were far less likely to experience blood sugar spikes and decreased fat burning after a late meal than their “early to bed, early to rise” counterparts.
• A 2016 study on 171 people also suggests that eating in line with your chronotype may support metabolic health. Night owls of normal weight were more likely to eat a higher percentage of their calories at dinner, while morning people of normal weight tended to eat more of their calories at breakfast and lunch. On the other hand, the overweight and obese subjects in both groups tended to eat in a way that was misaligned with their chronotype.

While many studies on meal timing suggest a net harmful effect of late-night eating (particularly related to altered glucose and fat metabolism, hunger hormone dysregulation, and subsequent impact on body weight), the majority have been conducted on a small number of people. This suggests a need for more extensive randomized controlled trials to confirm these findings and tease out the specific mechanisms driving them. Additionally, as the chronotype research highlights, findings from this type of research may be more helpful and allow for more tailored nutrition advice if participants are further broken down by “morning person” or “night owl.”

How to buffer the metabolic effects of late-night eating.

Sometimes, your only option is to have a meal close to bedtime. In that case, you may be able to reduce the adverse effects with these expert-backed tips.

Keep evening portion sizes reasonable: While you don’t want to go to bed hungry, you also don’t want to go to bed too full, as both scenarios can compromise sleep quality, which is closely tied to metabolic health and blood glucose control. Large late-night meals are also more likely to negatively impact blood glucose than smaller ones. “I’m a fan of eating more calories earlier in the day when we’re more insulin sensitive and keeping dinners smaller, which also minimizes digestive distress,” says Atlas. The ideal calorie range for a late-night meal will depend on your individual needs, activity levels, and what else you’ve eaten that day. It may look like anything from a hefty snack to a smaller version of your typical meals.

Be mindful of macros and digestibility: Because insulin sensitivity declines in the evening, making you more prone to post-meal blood sugar spikes, being aware of your carb intake is key. Many intervention diets in the studies above featured late-night meals containing 45-55% carbohydrate, 15-20% protein, and 30-35% fat. This could be quite high in carbs for someone watching their metabolic health, so simply adjusting these ratios could significantly buffer the metabolic consequences and sleep-disrupting effects of a late-night meal. According to Atlas, you should focus on protein, healthy fats, and fiber for satiation, and minimize refined carbs that will lead to a blood sugar spike and crash. To further encourage sleep, which supports metabolic health, “pick something easily digestible so that you minimize digestive distress and acid reflux at night,” she says.

Consider the following: Cooked non-starchy veggies topped with a fried egg, plain Greek yogurt with berries and a drizzle of nut butter, seed crackers with hummus and olives, a slice of low-carb bread (e.g., Base Culture) with nut butter and half a banana, or low-carb sandwich roll-ups where you use sliced meat as a wrap for veggies like bell peppers, olives, and lettuce.

Resist the urge to overcorrect: If you eat late one night, you might be tempted to skip breakfast the next morning to compensate—but studies don’t necessarily support this, and delaying your food intake might just prompt you to eat late again the following night. Some research suggests that a late dinner coupled with skipping breakfast is associated with worse glycemic control among people with Type 2 diabetes. A better strategy for metabolic health: Use the next day to reestablish the healthy eating habits you want to maintain over the long term. This might look like eating more calories in the first half of the day and having a smaller, balanced evening meal at least three hours before bed.

Consider a 12-hour overnight fast: If late-night eating is your norm and not just a one-off occurrence, you can always consider implementing a 12-hour fast between dinner and breakfast the following day. For example, if you eat dinner at 10 pm, wait until 10 am for breakfast. Several studies suggest that 12 hours is when your body starts to see benefits from fasting, like burning ketones instead of glucose.