One meal a day
Only small crossover trials in normal-weight adults have tested one meal a day. At the same calories, fat mass fell against three meals a day. Glucose results were mixed, with higher fasting glucose and poorer morning glucose tolerance in one trial. Blood pressure, LDL cholesterol and hunger rose. No trial in people with obesity was located.
- Status
- A dietary pattern, not a regulated product.
- Also called
- OMAD, one meal a day, one meal per day, single daily meal, 23:1, 22:2, 23:1 fasting
- Followed for
- weight loss, fat loss, blood sugar, insulin sensitivity, longevity
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help1
Reported risks3
- LimitedOne small crossover trial found blood pressure and total, LDL and HDL cholesterol rose on one daily meal against three meals at the same calories.How often is not known
- LimitedOne small crossover trial found hunger rose on one daily meal, and ghrelin, a hunger hormone, rose in the same trial.How often is not known
- LimitedLimited evidence: short trials found no loss of strength or aerobic capacity, though in an 8-week training trial only the group eating normally gained lean tissue.How often is not known
What people follow it for, and what was found
Shown to help1
Weight and fat mass
Small crossover trials found one daily meal lowered fat mass against three meals at the same calories, in normal-weight adults over 11 days to 8 weeks.
Compared with eating every day, with no fasting days or daily fasting window
The numbers and sources
- Effect
- Eating all maintenance calories in one meal a day for 8 weeks reduced fat mass against three meals a day, with body weight kept within 2 kg [1]. Over 11 days, one evening meal lowered body mass 1.4 kg against 0.5 kg on three meals (p 0.03) and fat mass 0.7 kg against 0.1 kg (p 0.049) [2].
- Population
- Healthy normal-weight middle-aged adults in a randomized crossover trial with two 8-week periods [1]; 13 lean adults enrolled and 11 completed, mean age 31 and BMI 24 [2].
- Sources
- [1], [2]
- Caveats
- Very small, short trials in lean adults. The abstract of [1] gives no participant number or size of the fat loss. No trial of one meal a day in people with overweight or obesity was located.
Mixed results1
Blood sugar
Limited evidence: one small trial found higher fasting glucose and poorer morning glucose tolerance on one daily meal, and another found lower glucose later in the day.
Compared with eating every day, with no fasting days or daily fasting window
The numbers and sources
- Effect
- On one meal a day eaten between 4 and 8 p.m., morning fasting glucose was higher, glucose rose more and stayed high longer in a morning glucose tolerance test, and the insulin response was delayed, against three meals. The changes reversed after the diet ended [3]. On one evening meal for 11 days, plasma glucose was lower during the second half of the day [2].
- Population
- Healthy normal-weight middle-aged men and women in a randomized crossover trial [3]; 11 lean adults [2].
- Sources
- [2], [3]
- Caveats
- Neither trial included people with diabetes. Glucose was measured at different times of day in the two trials [2][3].
Not shown to help1
Longevity
Limited evidence: in two large cohorts, adults who ate one meal a day had higher death rates than those who ate three meals a day.
Compared with people who ate three meals a day [5][6]
The numbers and sources
- Effect
- In 24,011 US adults aged 40 or older followed through 2015, eating one meal a day was linked to higher all-cause mortality (HR 1.30, 95% CI 1.03 to 1.64) and cardiovascular mortality (HR 1.83, 95% CI 1.26 to 2.65) than eating three meals a day [5]. In 148,438 South Korean adults aged 40 or older, the once-a-day group had higher all-cause and cancer mortality than the three-meals group, partly explained by waist size [6].
- Population
- 24,011 US adults in NHANES 1999 to 2014, 4,175 deaths [5]. 148,438 South Korean adults in the Korean Genome and Epidemiology Study [6].
- Sources
- [5], [6]
- Caveats
- Observational. Meal pattern was reported once, by 24-hour recall [5] or food questionnaire [6], and people who eat one meal a day may differ in health, work or income. Illness can also cause people to eat less often. No trial has measured lifespan on one meal a day.
How trials defined it
Trials gave all the calories needed to keep weight stable, either in one meal or in three meals a day. One trial served the single meal between 4 and 8 p.m. in two 8-week periods separated by an 11-week break [1][3]. Another served it between 5 and 7 p.m. for 11 days per period [2]. A related training trial allowed all food within a 4-hour window on 4 days a week, with no limit on amounts or types of food, alongside resistance training 3 days a week for 8 weeks [4].
Risks
Reported risks2
Higher blood pressure and cholesterol
One small crossover trial found blood pressure and total, LDL and HDL cholesterol rose on one daily meal against three meals at the same calories.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- On one meal a day, blood pressure and total, LDL and HDL cholesterol rose significantly against three meals a day, and cortisol fell [1].
- Population
- Healthy normal-weight middle-aged adults, crossover with two 8-week periods [1].
- Sources
- [1]
- Caveats
- The abstract gives no sizes for these changes. The authors note diurnal variation may affect the results [1].
Hunger
One small crossover trial found hunger rose on one daily meal, and ghrelin, a hunger hormone, rose in the same trial.
The numbers and sources
Mixed results1
Muscle and strength
Limited evidence: short trials found no loss of strength or aerobic capacity, though in an 8-week training trial only the group eating normally gained lean tissue.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- One evening meal for 11 days did not impair aerobic capacity or strength, and fat oxidation during exercise rose [2]. In young men doing resistance training, a 4-hour eating window on 4 days a week cut intake about 650 kcal on those days and did not change total body composition. Muscle cross-sectional area and strength rose in both groups, and effect sizes showed a lean soft tissue gain of 2.3 kg only in the group training without the window [4].
- Population
- 11 lean adults [2]; recreationally active young men over 8 weeks [4].
- Sources
- [2], [4]
- Caveats
- The training trial restricted eating 4 days a week, not daily [4]. Both trials were small and short.
Sources
- Stote KS, Baer DJ, Spears K, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. The American Journal of Clinical Nutrition. 2007. https://doi.org/10.1093/ajcn/85.4.981
- 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. Frontiers in Physiology. 2022. https://doi.org/10.3389/fphys.2021.771944
- Carlson O, Martin B, Stote KS, et al. Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women. Metabolism. 2007. https://doi.org/10.1016/j.metabol.2007.07.018
- Tinsley GM, Forsse JS, Butler NK, et al. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European Journal of Sport Science. 2017. https://doi.org/10.1080/17461391.2016.1223173
- Sun Y, Rong S, Liu B, et al. Meal Skipping and Shorter Meal Intervals Are Associated with Increased Risk of All-Cause and Cardiovascular Disease Mortality among US Adults. Journal of the Academy of Nutrition and Dietetics. 2023. https://doi.org/10.1016/j.jand.2022.08.119
- Tan LJ, Shin S. Mediating effects of waist circumference and BMI on the association between meal frequency and mortality. Public Health Nutrition. 2025. https://doi.org/10.1017/s1368980025000357