Excess body fat elevates the risk for a number of health issues, such as insulin resistance, diabetes, and cardiovascular disease. Obesity has been linked to several cancers, including esophageal, kidney, pancreatic, post-menopausal breast cancer, colorectal, and uterine cancers.
Weight loss interventions largely focus on reducing dietary energy intake and increasing energy expenditure through increased physical activity. However, a complex array of factors, beyond diet and exercise, can affect energy balance in the body and contribute to obesity.
An emerging field of research, known as chrono-nutrition, has found that timing of meals can have wide implications on your health. In terms of weight loss, when you eat has been shown to be just as important as what you eat.
Background to chrono-nutrition:
To make sense of the importance of when to eat, one has to understand the importance of the body’s master biological clock that is built into the brain. The biological clock regulates the body’s 24-hour biological rhythm, also known as the circadian rhythm, derived from the Latin phrase “circa diem”. This is a self-control system that prepares the body for expected changes in the environment like night and day, for example preparing the body when it’s time to sleep, typical times to eat, and body temperature changes.
Circadian rhythms are 24-hour cycles which form part of the body’s internal clock, running in the background to carry out essential functions to ensure that biological processes are optimized at various points during a 24-hour period. Apart from controlling the sleep-wake cycle, circadian rhythms for example also prompt the digestive system to produce proteins to match the typical timing of meals, as well as affecting the endocrine system which regulates hormones, in particular leptin the satiety hormone (which suppresses hunger) and ghrelin the hunger hormone.
Why is meal timing important?
Many studies have highlighted that the type of diet, levels of exercise, and emotional factors all contribute to differences in weight-loss effectiveness between individuals. Recent studies have indicated that the timing of meals may also play a major role in the success of weight-loss therapies. Not only what we eat, but also when we eat may play a significant role in weight loss and obesity treatment, as food timing can affect other circadian rhythm variables that are involved in weight loss.
Studies on meal timing:
A groundbreaking study published in 2019 – by the Department of Physiology at the University of Murcia in Spain – looked firstly at the effects of the timing of meals, and secondly at the impact on metabolism, glucose tolerance and obesity-related factors..
As Spain is notoriously known as the country where people eat late dinners, the latest in all of Europe at around 10 pm, this study concentrated on the effects of eating lunch earlier in the day rather than later in the day. This Spanish study found that the timing of lunch (eating an earlier lunch) was related to weight loss effectiveness.
Other studies published in 2021 and 2022 studied the effect of eating all meals earlier rather than later in the day, and found that eating an earlier dinner had the most significant effect on weight loss amongst overweight and obese participants.
Effects of late eating:
Eating during the body’s biological night can cause multiple metabolic changes:
The sleep-wake cycle: Late dinners have an adverse effect on the body’s biological clock, such as interfering with melatonin’s central role in the circadian system. Melatonin is a neurohormone that is nightly produced by the pineal gland, a tiny endocrine gland that is situated near the center of the brain, to prepare the body for sleep.
It plays a crucial role in regulating the body’s circadian rhythm. When activated at night, the pineal gland secretes melatonin into the bloodstream as well as into the cerebrospinal fluid around the brain and spinal cord, from where it is carried to all areas of the body. Receptors in the cells and tissue of the body detect the peak in melatonin being circulated at night and signals to the body that it is time to sleep and for various biological processes to slow down.
Melatonin levels from the pineal gland typically begin to rise around dusk and peak during the night at around 02:00, before falling to very low levels shortly before dawn.
Studies have shown that late dinners, within 2,5 hours of bedtime, with high levels of melatonin already present, impaired glucose tolerance, with an increased probability of glucose related metabolic alterations.
Circadian rhythm in hunger: There is a circadian rhythm in hunger and active ghrelin (the “hunger” hormone) are higher during the biological evening than during the biological morning. Studies found that late dinners caused ghrelin levels to spike while simultaneously suppressing levels of leptin, a hormone that signals satiety.
Energy balance: Studies found that late dinners resulted in participants burning fever calories and less fat, while fat cells stored more fat. One study found that when healthy young adults ate dinner at 10 pm instead of at 6 pm, they burned less fat and had a 20% increase in blood sugar levels. Eating late makes you less glucose tolerant and also makes the body burn less fat.
Insulin sensitivity: The body tends to be more insulin sensitive early in the day, which means muscles are better able to absorb and utilize glucose from the bloodstream. At night the beta cells in the pancreas, which produce insulin, become sluggish and are less responsive to elevations in blood sugar.
Blood lipids (fat): Studies found that late dinners induce glucose intolerance, reduced fatty acid oxidation and mobilization; increased plasma cortisol levels, lowered circulating free fatty acids, and delayed peaks in triglycerides.
Studies also found that the enzyme, called hormone-sensitive lipase, which releases fat from our body cells for energy, and which are typically more active at night, are suppressed when eating a late dinner. This means the body is prevented from burning fat at night.
A biopsy of subcutaneous white fat tissue taken from participants, both during early eating and late eating protocols, showed significant differences in fat metabolism. Late eating downregulated several genes that are responsible for fat breakdown, while increasing energy uptake in the form of fat storage in fat cells.
Core body temperature: A study measured core body temperature continuously across the full 24-hour sleep/wake cycle during the study period and found that late eating significantly reduced the average 24-hour core body temperature. This may have been due to the decrease in energy expenditure across the 24-hour cycle caused by late eating.
Strategies to follow an early-eating schedule:
- Skipping breakfast (usually due to job demands) increases the risk of obesity. The body is primed to metabolize food in the mornings.
- It is better to eat carbohydrates, for example simple carbs such as bread, pasta, and pastries, in the morning or early afternoon when the body is most insulin sensitive.
- Try to eat dinner early in the evening, at least two to three hours before going to bed.
- Make dinner the smallest meal of the day, with breakfast and lunch the biggest meals of the day. Shift most of the calorie rich foods to breakfast and lunch.
- It may not always be practical to eat an early small dinner every single day. People who manage to eat a light dinner at least five days a week still gain better blood sugar control and less daily fatigue.
Conclusion:
The timing of food intake can play a crucial role in obesity and weight loss treatment. Late dinner eating is linked to having a high body mass index (BMI) and high body fat percentage, while increasing the risk of obesity five times.
Modifying the time of day when we eat is a potential tool to assist with weight loss, in conjunction with healthy diet and lifestyle interventions.
References:
The best time to eat breakfast, lunch, and dinner according to the experts – here’s how the timing of your family meals can boost your health. Published 30 January 2024. GoodtoKnow. (www.goodto.com)
Timing of breakfast, lunch, and dinner: Effects on obesity and metabolic risk. Published November 2019 in the journal Nutrients. PubMed Central. National Centre for Biotechnology Information. US National Library for Medicine. National Institutes of Health. USA. (www.ncbi.nlm.nih.gov)
It’s not just what you eat, but the time of day you eat it. Published 10 January 2023. The Washington Post. (www.washingtonpost.com)
Metabolic effects of a late dinner in healthy volunteers – a randomized crossover clinical trial. Published 1 August 2020 in The Journal of Clinical Endocrinology & Metabolism. PubMed Central. National Centre for Biotechnology Information. US National Library for Medicine. National Institutes of Health. USA. (www.ncbi.nlm.nih.gov)
Timing is everything, right? Meal impact on circadian related health. Published 23 January 2023 in The Journal of Clinical Endocrinology & Metabolism. PubMed Central. National Centre for Biotechnology Information. US National Library for Medicine. National Institutes of Health. USA. (www.ncbi.nlm.nih.gov)
Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity. Published 4 October 2022 in the Clinical and Translation Report. Volume 34. Issue 10. Cell Metabolism. (www.cell.com)
How does obesity cause cancer? Published June 2017. MD Anderson Cancer Center. The University of Texas. (www.mdanderson.org)
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