OMAD Benefits and Results, Checked Against the Trials

OMAD Benefits and Results, Checked Against the Trials

The claimed OMAD benefits rest on two small crossover trials, one 12-month window study (not true OMAD), and one large observational cohort. Both crossover trials found lower fat mass when subjects ate one meal instead of three at matched calories. One also found higher blood pressure, higher LDL cholesterol, and more hunger.

Key Takeaways

• Two randomized crossover trials (Stote 2007, Meessen 2022) found modest fat-mass reductions on one meal a day at matched calories. Both were small: Meessen had 11 completers, and Stote's abstract does not give its sample size.
• Stote 2007 also recorded higher blood pressure, higher total and LDL cholesterol, more hunger, and lower cortisol on the single-meal arm.
• A 12-month NEJM trial (Liu 2022, n = 139) found no significant difference between calorie restriction with an 8-hour eating window and calorie restriction alone.
• An observational study of 24,011 U.S. adults (Sun 2023) linked one meal a day with 30% higher all-cause and 83% higher cardiovascular mortality, but this is association from a single dietary recall.

What OMAD Actually Means

OMAD is time-restricted eating where all daily calories go into one meal, usually inside a 1- to 2-hour window. Meessen's protocol placed it at 17:00 to 19:00, making it roughly 22:2. The remaining hours are a fast with zero-calorie drinks (water, black coffee, plain tea). Jumping straight from a standard schedule to 23:1 is a large shift; narrowing gradually from 16:8 or 18:6 is more sustainable.

OMAD Benefits the Trials Actually Found

Human studies only. Two are randomized crossover trials of OMAD; one is a 12-month trial of an 8-hour window; one is an observational cohort.

Stote 2007 found lower fat mass on one meal a day, but blood pressure rose and total, LDL, and HDL cholesterol all increased. Hunger climbed too. Subjects kept body weight within 2 kg because calories were locked.

Meessen 2022 found 1.4 kg body-mass loss versus 0.5 kg and 0.7 kg fat-mass loss versus 0.1 kg over 11 days. Fat oxidation during exercise increased with no drop in aerobic capacity or strength.

Liu 2022 (NEJM) is not OMAD but matters. An 8-hour window with calorie restriction produced 8.0 kg of weight loss over 12 months versus 6.3 kg for calorie restriction alone. The net difference of 1.8 kg was not significant (P = 0.11), so the window added no significant benefit beyond eating less.

The Downsides in the Same Data

Stote's crossover is the clearest warning: alongside the fat-mass reduction, blood pressure climbed and total, LDL and HDL cholesterol rose. Hunger increased as well.

Sun 2023's cohort of 24,011 adults found that those eating one meal a day had 30% higher all-cause mortality (HR 1.30, 95% CI 1.03 to 1.64) and 83% higher cardiovascular mortality (HR 1.83, 95% CI 1.26 to 2.65). This was based on a single 24-hour dietary recall and cannot prove OMAD caused the higher mortality, but it should temper any assumption that meal-skipping is protective.

OMAD Results: What to Expect in the First Month

In the trials, weight changes ran about 1 kg over 11 days to 8 weeks at matched calories. Most real-world OMAD weight loss comes from eating fewer total calories, not from a timing advantage. The NEJM trial reinforces this. Expect to feel hungrier, as Stote's subjects did on one meal a day. Short-term exercise capacity and strength held up in Meessen.

How to Do OMAD Without Wrecking the Day

Pick a consistent meal time. Build it around protein, vegetables, a starch or whole grain, and a fat source. A registered dietitian can help you size the meal.

Five OMAD meal ideas:

• Grilled salmon, roasted sweet potato, sautéed greens, olive oil
• Chicken thighs, brown rice, mixed salad, avocado
• Beef stir-fry with bell peppers, broccoli, jasmine rice
• Lentil stew with root vegetables, yogurt, flatbread
• Baked cod, quinoa, roasted Brussels sprouts, walnuts

Drink water and plain tea through the fast. If you feel dizzy or faint, stop the fast and eat.

Coffee and Caffeine on OMAD

Black coffee is roughly 2 to 5 calories per cup and generally accepted during a fast. Caffeine itself has zero calories. Milk, cream, sugar, or flavored syrups end the fast. Time caffeine early in the fasting window, keep the last dose at least 8 hours before bed, and keep total intake under the FDA's 400 mg daily guideline. Whether sweeteners disrupt a fast is a separate question: see do caffeine pouches break a fast and what to drink while fasting.

Who Should Not Do OMAD

• People on insulin or glucose-lowering drugs. Extended fasting raises hypoglycemia risk, as MedStar dietitian Laurie Hall, MS, RDN, notes. Talk with your healthcare team first.
• Pregnant or breastfeeding individuals. Calorie and nutrient needs are elevated.
• Anyone with a history of eating disorders. A 23-hour restriction can reinforce disordered patterns.
• People under 18. Growing bodies need consistent fueling.
• Anyone with heart disease or high blood pressure, given the Stote trial's blood-pressure findings. Consult your clinician.

If you take any medication or manage a chronic condition, discuss fasting with your prescriber.

Is OMAD Worth Trying?

Two small trials show OMAD can reduce fat mass at matched calories. The effect is modest. Stote's data carry a clear caution: blood pressure and LDL moved the wrong direction. The NEJM trial suggests the eating window is not the active ingredient; eating less is. OMAD is a calorie-control tool with trade-offs worth monitoring, not a metabolic shortcut.

Related from Roon

• Best pouches for fasting
• Does coffee break a fast?
• Why fasting makes you tired
• Does apple cider vinegar break a fast?

Frequently Asked Questions

Does OMAD burn fat?

Both crossover trials found fat-mass reductions at matched calories. Meessen 2022 recorded 0.7 kg fat-mass loss over 11 days versus 0.1 kg on three meals. But the NEJM 12-month trial found that restricting the window added no significant fat loss beyond calorie restriction alone. Most real-world OMAD fat loss likely comes from eating less overall.

Is OMAD healthy long term?

The OMAD trials covered here ran for 11 days and 8 weeks, so long-term data are thin. Sun 2023's NHANES analysis linked one meal a day with higher all-cause and cardiovascular mortality, though that is observational data from a single dietary recall. Stote found unfavorable blood-pressure and cholesterol shifts. Long-term safety remains an open question.

Can I drink coffee on OMAD?

Black coffee (roughly 2 to 5 calories per cup) is generally accepted during the fast. Milk, cream, or sugar break it. Stay under the FDA's 400 mg daily caffeine guideline and time the last serving well before bed.

What should my one meal include?

Protein, vegetables, a starch or whole grain, and a fat source. Fitting a full day of nutrition into one sitting is the core challenge. A registered dietitian can help size the meal to your needs.

How long until OMAD results show?

In Meessen 2022, measurable body-mass and fat-mass differences appeared in 11 days at matched calories. Outside a lab, most people also eat fewer total calories on OMAD, and that, not meal timing, drives most of the change on the scale. Individual variation is large.

One Pouch for the Long Stretch

A 23-hour fast is a long time to stay sharp, and a morning of coffee refills can feel like a spike and a fade. A Roon pouch has zero calories and zero sugar (it does contain sucralose; the fasting-pouch breakdown covers how that fits your protocol). Inside: 80 mg of caffeine with 60 mg of L-theanine for a calm start, plus 25 mg of methylliberine (Dynamine) and 5 mg of theacrine (TeaCrine).

The duration comes from methylliberine, which slows caffeine clearance. A randomized, double-blind crossover PK study (n = 12) found that co-administering the two cut caffeine's oral clearance from 41.9 to 17.1 L/hr and extended its half-life from 7.2 to 15 hours, with no increase in peak concentration (study). That study used 100 mg methylliberine and 150 mg caffeine, about 4x and 1.9x Roon's doses, so the mechanism points the same direction but the exact magnitude does not transfer. A 15-hour half-life is clearance data, not 15 hours of felt energy; Roon's window runs 6 to 8 hours. Place one under the lip in the morning and it covers a large part of the fast. Finish your last pouch at least 8 hours before sleep, use no more than 4 a day, and keep caffeine from all sources under the FDA's 400 mg figure. Roon costs from $9.16 per tin on a 12-tin subscription, with a 30-day money-back guarantee on a first order. Try Roon.

Sources

• Stote KS et al. "A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults." Am J Clin Nutr 2007;85(4):981-8. PubMed
• Meessen ECE 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. PubMed
• Liu D et al. "Calorie Restriction with or without Time-Restricted Eating in Weight Loss." N Engl J Med 2022;386(16):1495-1504. PubMed
• Sun Y et al. "Meal Skipping and Shorter Meal Intervals Are Associated with Increased Risk of All-Cause and Cardiovascular Disease Mortality among US Adults." J Acad Nutr Diet 2023;123(3):417-426. PubMed
• Hall L, MS, RDN. "Intermittent Fasting and Diabetes." MedStar Health, Aug 2026. MedStar Health
• FDA. "Spilling the Beans: How Much Caffeine Is Too Much?" FDA

Written by Roon Team