Can Eating Once A Day Lose Weight? | What Experts Say

Eating once a day (often called the OMAD diet) may lead to short-term weight loss by creating a calorie deficit.

You may have seen the claim that eating just one meal a day is a shortcut to rapid weight loss. It sounds convenient: skip breakfast, skip lunch, and eat whatever you want for dinner.

The diet, often called the OMAD or 23:1 fasting protocol, does usually create a calorie deficit, which is the basic math of weight loss. The honest catch is that this extreme approach carries some real, well-documented risks that make most health experts pause before recommending it for anything beyond a short-term experiment.

How OMAD Creates a Calorie Deficit

The main mechanism is straightforward: you squeeze your entire day’s food into a single meal eaten within a one-hour window. For most people, it is genuinely difficult to pack 2,000 or more calories into one sitting, especially if the meal includes vegetables, protein, and fiber.

This natural restriction is why many people see the scale drop in the first few weeks. It follows the same principle behind other time-restricted feeding schedules, just pushed much further. Weight loss on OMAD is primarily driven by calorie restriction and changes in how the body uses energy.

But the type of weight lost matters. A randomized controlled trial published in Nutrients, accessed via meal per day study, found that participants eating one meal lost more lean mass than those eating three meals across the day. Losing muscle is not ideal for long-term metabolic health.

Why “Just Eat Less” Can Backfire

The psychology of severe restriction often leads to a bounce-back effect. Extreme hunger is a powerful force, and the body is wired to resist what feels like starvation. Here is what often happens:

• Intense hunger and cravings: Fasting for 23 hours can trigger strong hunger pangs, making it hard to stick to the plan and increasing the risk of overeating during the one-hour window.
• Nutrient gaps: Packing all your vitamins, minerals, fiber, and protein into a single meal is a challenge. Over time, this can contribute to nutrient deficiencies that affect energy, skin, and immune function.
• Social isolation: Sharing meals with family or friends becomes nearly impossible. This social friction makes the diet harder to maintain and less enjoyable over the long run.
• Potential metabolic slowdown: Some research indicates that extreme caloric restriction may signal the body to lower its metabolic rate to conserve energy, which can make future weight loss harder.

These factors help explain why OMAD is generally not considered a sustainable long-term dietary strategy.

Risks That Override the Scale Victory

The number on the scale can be motivating, but it does not tell the whole story. As WebMD points out, relying on a single meal makes it hard to get enough protein and fiber, a known risk the day safety breakdown highlights. Losing lean mass is a significant downside that can lower your resting metabolism over time.

Beyond muscle loss, OMAD is explicitly not recommended for people with certain health conditions. Most experts advise against it for anyone with a history of eating disorders, pregnant or breastfeeding women, and those managing diabetes or other metabolic conditions.

The restrictive nature of the diet can also blur the line between structured eating and disordered eating. The evidence for OMAD is mixed, and the potential downsides make it a risky choice for most people.

Who Should Definitely Skip OMAD

Given the risks, this diet is not suitable for everyone. The following groups should avoid it entirely:

1. People with a history of eating disorders: The rigid 23-hour fast can trigger or worsen restrictive or binge-purge cycles.
2. Pregnant or breastfeeding women: Nutrient needs are significantly higher during these times, and a single meal makes it very difficult to meet those needs for both mother and baby.
3. Individuals with diabetes or blood sugar issues: Long periods without food can lead to dangerous drops in blood sugar in people on certain medications.
4. Those prone to gallstones: Prolonged fasting can increase the concentration of bile in the gallbladder, potentially raising the risk of painful gallstones.
5. Athletes or highly active people: Performance and recovery depend on a steady flow of nutrients. A single meal makes fueling workouts and repairing muscle challenging.

If any of these apply to you, OMAD poses more risk than reward. Your overall health depends on more than just the number on the scale.

A More Balanced Approach to Time-Restricted Eating

If you are drawn to the idea of intermittent fasting, there are gentler versions that carry fewer risks. A 16:8 schedule, where you eat within an 8-hour window, is often much easier to tolerate and sustain while still providing some of the metabolic benefits.

A 2025 review of the research noted that OMAD may offer some cardiovascular and metabolic improvements, but these potential benefits must be weighed against the known risks. The key is finding a pattern that fits your lifestyle without causing deprivation or stress.

For sustainable weight loss, focusing on whole foods, adequate protein, and fiber within a manageable eating schedule is the standard that most dietitians recommend. The goal is a healthier relationship with food that you can maintain for years, not just a few weeks.

The Bottom Line

Eating once a day can create the calorie deficit needed for short-term weight loss, but it comes with real risks. Loss of lean mass, potential nutrient deficiencies, and the difficulty of maintaining the routine make it a poor choice for long-term health.

If you are considering a major dietary shift like OMAD, a registered dietitian or your primary care provider can help you determine whether it is a good fit for your blood sugar levels, muscle mass goals, and personal health history.