Eating One Meal Per Day Without Reducing Calories Improves Body Composition and Metabolic Flexibility

From feeding coins into vending machines to rustling through snack drawers to tapping out a Postmates order within seconds, our modern-day lives provide access to copious amounts of food literally at our fingertips — no matter the time of day. Unlike our long-ago ancestors, who consumed in excess only when they came across a bountiful hunt or gathering session before fasting until the next feast came around, we are eating more — and more often — than ever.

Since many people can hardly go two hours without the next snack break, our digestive and metabolic processes constantly run without rest. This has led to a staggering prevalence of metabolic disorders, including excess weight and fat gain with blood sugar instabilities whose peaks and valleys could rival the world’s tallest roller coaster. 

As an alternative to reducing food intake to improve metabolic health, researchers have been studying forms of intermittent fasting, where the daily calorie count doesn’t change, but the window of eating is significantly shrunken. In a recent study, a Dutch-based research team looked at the metabolic health and body compositions of people who consumed all of their calories within just one meal per day. Authored by Meessen and colleagues from the University of Amsterdam, this research shows how forgoing three square meals per day in favor of a solo dinner feast leads to a greater loss of body fat and weight with improved metabolic flexibility.

The Metabolic Facets of Fasting 

Also known as OMAD, eating just one meal a day is a recent trend in the intermittent fasting world, in which people consume all of their recommended calories within a one- to two-hour period. (In this study, participants ate within two hours around dinnertime.) Restricting eating to a specific time without significantly reducing calories has been shown to exert more beneficial health effects without the downsides often seen with caloric restriction (CR). As the name suggests, CR reduces calorie intake by 15-40% and has been linked to lifespan extension in animal studies. Still, it can also lead to detrimental loss of lean body mass and disruptions to immune and hormone activity.  

Researchers are beginning to suspect that most of the benefits from fasting come from the prolonged periods between meals — not a reduction in food intake. Many people on a Western diet spend up to 16 hours per day in a postprandial (post-eating) state, causing the body to constantly work hard on transporting glucose (sugar) from the blood into cells. 

This continuous blood sugar shuttling is the body’s primary focus, leading to dietary fat being stored in adipose tissue rather than being broken down to be used as energy, a process known as fat oxidation. On the flip side, fasting periods allow for fat breakdown known as lipolysis, which switches the primary fuel source our bodies use for energy from glucose to fat,  lowering body fat stores in the process. This is known as metabolic flexibility, or the body’s ability to alter metabolism in response to what fuel source is available.

OMAD Benefits Body Composition and Fat Utilization

In this study, a small group of healthy young adults consumed one meal a day in the evening for 11 days, then ate three standard meals per day for 11 days, with a washout period in between to “clean the slate”. This study was crossover by design, allowing researchers to compare individual responses to the treatment (OMAD) versus control (three meals per day). Essentially, participants started off either with the OMAD diet or their standard diet, then crossed over to the other diet halfway through the study. Both the OMAD and control diets were similar in calories, which were adjusted individually based on gender, age, body size, and activity levels. 

Meeseen and colleagues found that the OMAD eating pattern led to a significant decrease in total body weight and fat mass. The participants lost 3 pounds (lbs) of body weight and 1.5 lbs of fat on OMAD, while the standard meal diet led to 1.1 lbs of weight loss and 0.2 lbs of fat loss. These benefits to body composition may come about from enhancements to lipolysis and shifting oxidation from glucose to fat during the fasting periods. 

This is supported by the results showing increased fat oxidation during exercise while on the OMAD diet. There were no noticeable impacts of OMAD on aerobic capacity or strength — which is a good thing, as fatigue or lost strength could be expected during fasting periods. Further, the solo-meal pattern lowered blood glucose levels during the second half of the day, although fasting glucose and post-meal sugar concentrations were unchanged. 

The research team speculates that more benefits may have been seen if the one meal per day was breakfast, not dinner. Early time-restricted eating (TRE) has been shown to improve glucose sensing and reduce body weight more than late-TRE in previous research. But, the metabolic and body weight-related improvements in this study were still impressive; as Meeseen and colleagues state, “​​These data show that the human body can cope with one large daily meal providing all the required energy, without deteriorating metabolic regulation.” 

One Meal Per Day Keeps the Body Fat Away

Although medications are often used to target dysregulated metabolic functioning, the authors of this study rightfully look to the benefits of using food first, stating, “Nutritional- and exercise interventions should be the first in prevention- or treatment strategies because of the biological rationale, low cost, and non-pharmacological approach.” 

While this study was small, Meeseen and colleagues are hopeful that larger-scale research will be done in the future to validate their findings — especially in people with dysregulated metabolisms or with low metabolic flexibility, who could potentially reap more benefits from this style of eating.

However, a caveat is that OMAD is notoriously difficult to consume one’s entire daily caloric needs in one shot, especially for people used to eating smaller meals throughout the day. Despite some research indicating that eating all of one’s calories in the morning may be better for metabolic health, feasting at dinner could feel more natural and easier to implement, as it benefits building up hunger throughout the day.

Overall, although “OMAD” is relatively new to the diet scene, our ancestors had been practicing this style of eating for centuries before we came along, and most people could benefit from emulating some of their fasting practices, like skimping on snacktime and holding off on your feast until later in the day. 

References: 

Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. 2019;11(6):1234. Published 2019 May 30. doi:10.3390/nu11061234

Meessen ECE, Andresen H, van Barneveld T, et al. Differential Effects of One Meal per Day in the Evening on Metabolic Health and Physical Performance in Lean Individuals. Front Physiol. 2022;12:771944. Published 2022 Jan 11. doi:10.3389/fphys.2021.771944

Pak HH, Haws SA, Green CL, et al. Fasting drives the metabolic, molecular, and geroprotective effects of a calorie-restricted diet in mice. Nat Metab. 2021;3(10):1327-1341. doi:10.1038/s42255-021-00466-9