When you eat carbs can be just as important as what type of carbs you're consuming.
Front-loading your calories — and specifically your carbohydrates — by eating them earlier in the day is one factor in optimizing your glucose response and metabolic rhythm.
Morning vs. evening glucose tolerance
Eating a majority of calories and carbohydrates in the first half of your day is a good way to take advantage of morning insulin sensitivity [1].
In other words, your body is more insulin sensitive earlier in the day, and less insulin sensitive later in the day. Increased insulin sensitivity means your body can use glucose more efficiently, resulting in steady blood sugar and energy levels.
For example, if you consume the same meal in the morning vs. evening, you’ll have a higher post-prandial (or post-meal) glucose response after the evening meal [2]. On top of that, symptoms of insulin resistance — such as cravings or fatigue — become more apparent later in the day despite eating the exact same meal.
In fact, eating earlier in the day has even been shown to help people with Type 2 diabetes manage their appetite and lose weight [1].
This is partially due to increased insulin secretion in the morning, which helps clear glucose from the bloodstream more rapidly — resulting in less glucose variability and fewer blood sugar spikes [1].
To demonstrate the variance in morning vs. evening variability, here is a 30-day average glucose summary from one Veri user.
Despite consuming most of her meals in the morning, you can see more variability after 1pm.
Optimizing meal timing by front-loading your carbs and calories allows you to maximize glucose tolerance and eat according to your circadian rhythm, which is largely responsible for the difference between morning and evening insulin sensitivity.
Cortisol and circadian rhythm
Besides insulin, cortisol is another hormone involved in glucose variability throughout the day.
Your body’s circadian clock is primarily influenced by your daily cortisol cycle. Circulating cortisol varies throughout the day with levels increasing in the late afternoon and early evening [3].
Elevated cortisol later in the day translates to increased insulin resistance and less glucose sensitivity. This response is exaggerated with age, so front-loading your daily calorie and carbohydrate intake can be especially beneficial later in life.
Even for shift or overnight workers, the pattern of better glucose tolerance in the early half of the day is clear [4]. Below is another 30-day average glucose summary of a nurse who works overnights, where you can clearly see the trend of lower glucose in the first half of the day compared to the second half.
Despite this user’s untraditional sleep routine, her glucose timeline mirrors that of the day-shift worker in Figure 1.
Regardless of sleep patterns, cortisol and insulin work in tandem according to biological circadian rhythms, which favor morning food intake as opposed to evening food intake.
Optimizing carbohydrate intake for your circadian rhythm
Recognizing how hormonal rhythms affect glucose levels throughout the day helps you capitalize on periods of increased insulin sensitivity.
For example, to best optimize your calorie and carbohydrate intake according to your circadian rhythm, you might try one or more of the following strategies:
- Go big with breakfast. Consider eating a larger breakfast and smaller meals for lunch and dinner.
- Eat low-carb after lunch. Front-load your carbohydrate intake to the early half of your day to minimize glucose spikes and variability.
- Don’t dine and doze. Avoid large meals before bedtime to optimize sleep and accommodate your natural circadian rhythm.
- Limit ultra-processed foods. Escape the blood sugar rollercoaster by filling up on glucose-friendly whole foods like meat, eggs, vegetables, fruit, and healthy fats.
- Exercise regularly. Physical activity helps increase insulin sensitivity, regardless of the time of day.
Kayla Girgen is an online Registered Dietitian and Certified Personal Trainer specializing in weight management and bariatric nutrition. Kayla’s holistic approach to weight loss helps you learn how to work with your body — not against it. With CGM, Kayla’s clients see first-hand how certain food, exercise, stress, and sleep impact their metabolism to maximize weight loss and metabolic wellness. Read more from Kayla on her blog.
