The big debate for decades has mostly been around what we should be eating — vegan vs. high carb, low fat vs. Mediterranean, and so on — but arguably, an equally important question is when should we be eating? Does the time of day we eat have an impact on our health? How about the frequency of meals and snacks? New research points in the direction of, yes, it likely does.
When You’re More Insulin Sensitive
Insulin sensitivity is a common term when thinking about diabetes, however, it has an impact on just about everyone. Insulin is a hormone in our bodies that is produced and released when certain nutrients are present in our blood, specifically carbohydrates and protein. When we consume food high in carbohydrates and/or protein, such as a hamburger, the pancreas responds by producing and releasing insulin into our blood stream. The insulin then helps shuttle these nutrients into our cells. When someone is insulin sensitive, insulin has a much easier time getting these nutrients into the cells.
On the contrary, when someone is insulin resistant, the cell is much less responsive to insulin knocking on its door and does not easily allow the glucose and amino acids (from protein) inside the cells. In response, blood glucose levels usually increase, and more insulin is produced. If this insulin resistant state happens too frequently and blood glucose and blood insulin remain high, it can lead to various chronic diseases such as type 2 diabetes.
Ideally, we want to be in a state of insulin sensitivity, which is easier on the body and reduces the risk of developing chronic disease.
Aside from what we eat, insulin sensitivity can also be influenced by exercise. Exercise has an impact on how our bodies utilize and store glucose. Glucose is the preferred fuel for the body. It requires less time, fewer metabolic processes to use, and is a quicker energy source compared to fats and protein. So, it’s no wonder that during exercise, glucose is usually the body’s go-to fuel.
Glucose is stored in our bodies as glycogen in our livers and muscles. During exercise, our bodies need glucose for the increased fuel demand, but also to maintain regular blood glucose levels for normal bodily functions. The increase with which glycogen stores are depleted is related to the intensity of the exercise performed. The higher the intensity, the more reliant the body is on glucose as its fuel. So, HIIT training and heavy weight training are two common types of exercises that deplete glycogen quicker.
When you eat a meal after glycogen-depleting exercise, you have more room in your storage. So, when eating carbohydrates that normally elevate blood glucose, more of that glucose will be transported to the liver and muscles to replete the glycogen stores instead of hanging around in the blood. So, when in a glycogen-depleted state after a workout, the same high-carb meal will produce less of a glycemic response (i.e., rise in glucose and insulin) compared to that same meal when in a glycogen-replenished state before exercising. If you’re considering having a cheat meal this week or deciding when to consume your high-carb food item, it’s likely best to do so after you work out.
Additionally, if you’re interested in increasing your body composition, a few studies have shown that exercising in a fasted state can increase your lipid (fat) oxidation. This can potentially contribute to more fat loss. Furthermore, having a post-exercise meal containing protein has been shown to increase myofibrillar protein synthesis, which contributes to overall muscle growth.
Timing your meals around exercise and planning what you will eat around that can have some positive health benefits. However, keep in mind that the response you have to that meal can also depend on the length of exercise, time of day, whether or not you have already eaten that day, how you respond to and utilize nutrients, your body composition, underlying health conditions, medications, and sleep schedule.
Early in the Day
Time restricted feeding (TRF) is a common fasting protocol used by many people for various reasons such as improved glycemic response, weight loss, and better energy. During TRF, food is consumed within a predetermined time frame, and the remaining hours of the day are spent fasting. A common protocol for TRF is to skip breakfast and not eat the first meal of the day until lunch/around noon and stop eating after dinner around 8pm, giving you a 16:8 TRF window (i.e., 16 hours of fasting and 8 hours of eating). However, recent research has come out arguing for a shift towards early TRF, or eTRF. This would mean having your first meal of the day around 8am and stopping eating around 2-4pm, depending on your feeding window. You would then skip dinner and not eat until 8am the next day.
One study took non-diabetic patients and randomized them into either the eTRF group (eating their meals from 8am-2pm) or the control group (eating their meals from 8am — 8pm). Both groups ate the same meals per day and only the feeding window was different. Results showed that the eTRF group had lower 24-hour glucose levels, lower glucose levels at night, lower insulin levels, and less glucose excretions (sharp elevations in glucose above normal). When the researchers looked at markers for circadian rhythm, they found that specific circadian clock genes such as SIRT1 and the autophagy gene LC3A were increased, and a more favorable cortisol pattern was seen in the eTRF group.
A second similar study looked at eTRF in pre-diabetic men. The experimental group restricted their food to a 6-hour feeding window and were required to have their first meal between 6:30–8:30am and their last meal no later than 3pm. The control group ate for a 12-hour period and consumed the same meals provided to the eTRF group. Results from the study showed that eTRF increased insulin sensitivity, improved beta cell function, lowered blood pressure and oxidative stress, and decreased the desire to eat in the evening, which may assist with weight loss and improve health overall.
Meal frequency has also been a common debate topic. Arguments for 3 meals per day, 3 meals and 2 snacks, 6 small frequent meals, one meal per day and intermittent fasting are common in the nutrition world. What we have found is that even though different meal plans can work for different people, in general, we probably don’t need as much as we think.
Proponents for 5–6 small meals per day argue that continuous food keeps the metabolism running at a higher rate and helps maintain better satiety throughout the day. For some people this may be true, but a few studies have been done to challenge this argument. One study showed no significant difference in weight loss while eating 3 meals plus 3 snacks per day compared to 3 meals per day. Another study showed that eating 6 small meals per day resulted in less feelings of being full.
In addition, 5–6 meals allow for more deviation from a whole food, healthy meal plan. Eating more frequently uses a lot more willpower and provides increased temptation to eat processed snacks, dessert, and sugary beverages. So aim for 3 meals per day, or even less if you practice intermittent fasting or time-restricted feeding. Sometimes 1 or 2 meals will be enough.
Only if You’re Hungry
Many of us still remember our parents scolding us to “not leave the dinner table until our plate is clean.” Of course our parents had the best intentions, and that was likely something that was passed down from their parents, however, the ideology that finishing everything that is in front of us has given us the false sense that we will be doing ourselves harm by not keeping our bodies full of food 24/7.
On the contrary, our bodies are intelligent machines that have built-in mechanisms to provide our cells with the energy they need even in times of fasting. We keep stores of energy in our bodies in the form of glucose, or sugar (as glycogen in our liver and muscles) and fat (as adipose tissue under our skin and around our organs). When in the absence of nutrients for a prolonged amount of time, our body can break down these stores and convert them into fuel used for energy. Just think of our hunter and gatherer ancestors who sometimes went days without eating, but still had enough energy to hunt and capture their prey. They utilized their own energy stores to fuel them in the pursuit of food.
Along with what you eat, when you eat can have similar contributions to your health. To help reduce your risk of chronic disease, improve body composition, and optimize circadian rhythm, consider eating earlier in the day compared to later, and time your meals—especially those higher in carbs and protein—after you work out. To assist with hunger levels and prevent overconsumption, think about reducing the number of meals you have per day. Finally, no need to eat if you’re not hungry. Your body will likely do just fine without that afternoon snack.