I am an advocate of a big breakfast, of living and eating with your circadian rhythms. Getting your day started early is in your best interest, metabolically and mentally. Eating more calories at breakfast may reduce overall calorie intake for the whole day. There is good science to back up my advocacy. Sleep/wake cycles, body temperature, hormone secretion and other functions are dependent on circadian rhythms. Research has long noted that meals in misalignment with your biological clock, or circadian rhythm disruption, is associated with an increased risk of chronic disease, such as obesity and diabetes. Our internal circadian rhythmicity is under the influence of day and night, and controls the hypothalamic–pituitary–adrenal axis (HPA axis) which produces regular diurnal secretion of hormones. Research is showing that you should eat with your circadian rhythm, with your biggest meal in the morning and your smallest at night. A review of U.S. national eating patterns found that people who eat breakfast eat healthier overall and weigh less. Eating late is associated with decreasing metabolism, the ability to breakdown carbohydrates and glucose tolerance, and a blunted cortisol response. Eating late may influence the success of weight-loss therapy. Not that anyone thought eating late, on the couch, while watching tv was a healthy idea, though I do admit sometimes it is in your mental health interest. Consistently skipping breakfast is associated with an over-active HPA axis, independent of stress, and over time can increase risk of cardiometabolic disease in some people.
All this makes a solid case for a big meal, i.e. breakfast, early in the morning, with the rising sun. It is how you are biologically programmed to eat. Your body is ready to absorb and metabolize food early. I know a lot of people say, “I can’t eat in the morning”. Hormones are secreted in a natural diurnal rhythm, and we override it by not eating in the morning. We have deprogrammed our natural cycle. Though people can be re-programmed! A review of research identifies the benefits of eating three meals a day, with a big breakfast, small dinner, no snacking, and increased consumption of fruits and vegetables. Start by eating breakfast, and then a bigger breakfast. A functional consideration is to test your cortisol with a saliva test, typically done four times over the day. If you are really out of alignment a before and after test can show you how much you’ve improved. Though most people will simply feel better and see metabolic improvements. What you eat is a synergistic combination of day and night, food and sleep, cortisol, melatonin, leptin, ghrein, and an array of other hormones and metabolites.
Here are few hormones to know:
Cortisol: Secreted in the morning
Peak cortisol is in the early morning. Released in response to stress and low blood-glucose. Coffee and smoking can cause cortisol to stay elevated. Cortisol raises free amino acids in the blood.
Melatonin: Secreted at night time. Increases in the evening and is highest at night during deep sleep. Inadequate melatonin impacts the sleep wake cycle. Melatonin is made from serotonin, which is made from the amino acid tryptophan.
Leptin: Secreted when you are full. The "satiety hormone", made by white adipose cells and inhibits hunger. It is secreted in a diurnal rhythm with lower levels in the morning and higher levels at night. Levels are positively correlated with fat mass.
Ghrelin: Secreted when the stomach is empty. The "hunger hormone", also known as lenomorelin is produced by cells in the gastrointestinal tract and regulates appetite, as well as the distribution and use of calories. Research has shown an inhibitory effect of sleep on ghrelin secretion.