What’s the best time to eat dinner? That all depends on what your goals are. For the purpose of this discussion, we’ll stick to better blood glucose control.
For the most part, earlier is better. But it’s important to point out that earlier means different things to different people.
For an early bird who goes to bed at 10pm, a 5pm dinner is rational. But if you’re more of a night owl, that can be 7-8 hours before bedtime.
A new paper shines a light on how when we eat our last meal impacts blood glucose regulation. It also confirms previous data on how circadian rhythms regulate our blood glucose.
You can check out the specifics in our latest video on Youtube:
Best time to eat dinner based on the data
The cool thing about this paper is that it looks at the best time to eat dinner in relation to bedtime. They took people and had them do an oral glucose tolerance test either 1-hour or 4-hours before bedtime.
This is important as both may be important. Melatonin plays a role in blood glucose regulation, as we’ve discussed in a blog you can check out here.
So both the specific time of day and its relation to when you go to sleep are important. Our light exposure regulates melatonin output, which should be consistent day to day.
We don’t really know which one is more important. However, a recent paper took a look at night shift workers who shifted their eating to the day. Night shift workers who ate during day vs night had blood glucose levels 6.3% lower than those that ate at night.
In the paper we discuss in the video, people consumed 75g of glucose both 1- or 4-hours prior to bedtime on separate days. This tells us how well we process carbohydrates during our last meal in relation to bedtime.
The results indicate that the best time to eat dinner in reference to sleep time was 4-hours prior to bed. Eating 1-hour prior to bed vs 4-hours led to 6.7% lower insulin auc and 8.3% higher glucose.
Interestingly, melatonin levels were 3.5-fold higher 1-hour before bed vs 4-hours. This jibes with recent data on melatonin and its relation to insulin.
How melatonin impacts the best time to eat dinner
Several lines of evidence indicate that melatonin plays a role in blood glucose regulation. People with a genetic polymorphism in the melatonin 1b receptor have impaired glucose tolerance. Consequently, this increases their risk of types 2 diabetes.
One study indicates a daytime and evening supplemental 5mg dose of melatonin impairs blood glucose regulation in women.
Another found taking a larger 9mg dose right before bedtime improves insulin sensitivity.
And another paper looked at common gene that increases Type 2 diabetes risk. The G allele in the melatonin 1b receptor(MTNR1B, rs10830963) increases expression of the melatonin receptor in the pancreas.
As a result, people with this allele see a stronger inhibition of insulin by melatonin.
This data indicates that the circadian rhythm of melatonin helps regulate glucose. As we get closer to bedtime at night, melatonin increases to inhibit insulin secretion.
Since we don’t eat when we sleep, this prevents insulin from crashing blood glucose. As a result, melatonin also increases insulin sensitivity during the daytime.
Based on this data, the best time to eat dinner is around 4 hours prior to bed. In addition, it should be earlier in the day while light levels are still sufficient to inhibit melatonin.
When to eat carbohydrates and protein
The interesting thing about this data is it also tells us when to eat our carbs. If your goal is controlling blood glucose, earlier is better. Of course, other factors play a role in dictating this as well. When you’re most physically active in particular.
It also indicates that eating protein earlier in the day may benefit muscle mass. A recent paper found that muscle protein synthesis is greater during the day. Consequently, muscle breakdown is greater at night.
This may also be under the control of insulin. Insulin increases muscle protein synthesis when total blood amino acids are elevated. This means that protein feeding during the day should increase muscle protein synthesis compared to at night when insulin is suppressed.
Of course, since exercise increases muscle protein synthesis, exercise type and timing is also important.
Various factors play a role in determining the best time to eat dinner. It also depends on your goals. If your goal is to optimize blood glucose management, an earlier dinner 4 hours prior to bed is best.
Interestingly, it also implies that eating carbohydrates earlier in the day will lead to better glucose control. Furthermore, if your goal is to optimize muscle mass, consuming protein earlier vs later may increase muscle protein synthesis.
In the long term, higher muscle mass also helps you better regulate blood glucose levels. That is, provided you continue to use it.