Meal Timing and Metabolic Health

Eat the same number of calories for better metabolic health

Hit a home run: Eat more calories earlier in the day by shifting your food intake from dinner to lunch and/or from lunch to breakfast. Also, shift your calories from sugars and starches to vegetables, fruits, beans, and nuts. You can improve your metabolic health with the simple tactics of shifting your eating habits. No need to cut or count calories.

Shift your food intake to earlier in the day to lose weight

A study in Spain provides evidence that timing of eating influences whether you gain or lose weight. Persons with overweight or obesity (N=420) at weight loss clinics in southeastern Spain participated in a weight loss program that featured the Mediterranean diet and behavioral and cognitive techniques. Over a 20-week period, participants who ate lunch (the biggest meal of the day) before 3:00 pm lost significantly more weight (about 2.1 kg) than participants who ate lunch after 3:00 pm. Surprisingly, both groups had similar energy intake, dietary composition, appetite hormones, sleep, and physical activity. Reasons for greater weight loss for the earlier eaters were unclear. Possibilities include genetic differences and better circadian system function.

Align your food intake with your circadian rhythms

The positive results of shifting food intake may reflect circadian (daily) rhythms of metabolism that govern, among other things, whether you burn or build fat in your body. While the details remain murky, studies of lab animals and now humans strongly indicate that moving consumption of food, especially fat and protein, to earlier in the day promotes better health. The photo shows what I typically eat for lunch—a lot of veggies and fruit complemented with hummus, almond butter, yogurt, and bran. Skipping breakfast to cut calories appears to be totally counterproductive. Shifting your food intake to earlier in the day sounds almost magical: Eat the same number of daily calories as you do now, but shift them towards breakfast and lunch and away from dinner—and lose weight. Why not give it a try?

Recent research identified a novel factor, circadian rhythm, which appears to affect the ability to maintain a healthy weight or lose weight. Circadian rhythm refers to physical, mental, and behavioral processes that align with a 24-hour cycle. The suprachiasmatic nucleus in the brain’s hypothalamus serves as the central clock. Peripheral clocks exert control over various organs including the heart, liver, and pancreas. (Did you know that your liver has a clock?) Food consumption appears to synchronize peripheral clocks. Thus, the timing of food intake, along with its nutrient content, may affect the physiology of digestion and metabolic health. Eating at certain times may uncouple peripheral clocks with the central clock. Some evidence points to impaired digestion following ingestion of a high-calorie food after an evening meal. Body fat appears to operate under a circadian clock. Timing of eating, along with its nutrient content, may affect whether your body stores or mobilizes fat, with potential metabolic implications.

Time-restricted eating

Animal studies show that time-restricted feeding leads to a robust circadian rhythm and predicts several health benefits, including weight loss, longer sleep duration, reduced systemic inflammation, and reduced cardiac aging. Researchers at the Salk Institute in California developed a cell phone app to monitor what and when healthy human adults ate. Most subjects ate erratically and frequently throughout the day, counter to the assumption of three meals per day. Less than 25 percent of calories were eaten prior to noon; more than 35 percent were eaten after 6 pm.

A subset of the subjects participated in a restricted feeding study in which they limited food intake to 10-11 hours per day (say, from 7 am to 6 pm) for 16 weeks. Although researchers did not advise subjects to otherwise alter their eating, subjects reduced their daily caloric consumption by 20 percent. Subjects also lost an average of 3.3 kg of body weight, reported better sleep, reduced hunger at bedtime, and greater energy. Thirty-six weeks after the study ended and after no further contact with the researchers, the subjects still exhibited these same health improvements. Shifting food consumption to earlier in the day and eliminating eating after 6 pm could be a simple yet powerful way to live better.

Big Breakfast, Little Breakfast

In a study from Israel, middle-aged obese or overweight, sedentary subjects were randomly assigned to eat the Big Breakfast, which was rich in fat and protein and contained 33 percent of daily calories. The other participants ate the Small Breakfast, which was rich in carbohydrates and contained 12.5 percent of daily calories. Both the Small and Big Breakfast participants’ diets had the same number of total daily calories, which was 500 calories less than that required to maintain a stable weight. Over three months, subjects consumed about 150-200 more calories per day than recommended, with no significant difference between the two diets.

After three months, subjects in the Big Breakfast group has significantly lower systolic blood pressure, HbA1c (blood sugar over the previous 2-3 months) than those in the Small Breakfast group. Body weight, body-mass index, waist circumference, and hip circumference all declined similarly in both groups. A significantly greater proportion of the subjects in the Big Breakfast group reduced their daily dose of diabetes medication, and a significantly greater proportion of those in the Small Breakfast group increased their diabetes medication dose. Hunger—satiety scores were significantly higher (meaning less hunger and greater satiety) for the Big Breakfast group. Can you imagine shifting some of your dinner calories to breakfast with meal timing? If so, you may enjoy better metabolic health.

Timing of eating and overweight / obesity

Preliminary evidence suggests a link between timing of food intake and human obesity, independent of total energy intake, dietary composition and estimated energy expenditure. Finding the most opportune time to eat may complement how much and what to eat from a weight management standpoint. Emerging evidence suggests that inopportune meal timing creates metabolic impairments via disrupting circadian rhythms. A systematic review of observational and experimental studies in humans by Italian researchers found that eating earlier during the day predicted health benefits, including less weight gain, lower blood sugar, and lower risk of diabetes mellitus. Earlier meal timing may provide an opportunity to improve metabolic health and maintain a healthy weight.

New evidence that earlier eating improves metabolic health

Recent studies suggest that shifting food consumption from later to earlier in the day fosters weight loss and possibly weight loss maintenance. Corroborating evidence comes from a new systematic review and meta-analysis of 9 randomized clinical trials, all except one of which occurred in free-living conditions. By coincidence, all of the studies included energy-restricted diets. Participants who shifted their food intake to earlier in the day showed a modest but significantly greater weight loss (1.23 kg) compared to participants who didn’t make that shift. Shifting food intake to earlier in the day also led to improved metabolic factors including reduced insulin resistance, lower blood glucose, and LDL-cholesterol. The included studies ran for relatively short time spans (up to 16 weeks), thus long-term acceptance of shifting food intake to earlier in the day and its effects of body weight without concomitant caloric restriction remain unknown. Nonetheless, eating more for breakfast and/or lunch and less for dinner seems doable for many people and may help you maintain a healthy body weight. Why not give it a try?

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