Almost everyone’s serving a new diet nowadays. As a result, it can be hard to keep track of what’s an unhealthy fad versus sound nutritional advice. But knowing the difference can be vital in helping patients nourish their bodies in healthy ways—and gain, lose, or maintain necessary weight.

One of these trending diets is the “One Meal A Day” diet, also known as OMAD. Like its name implies, OMAD involves eating a single meal—and nothing else—each day. Dietitians have different takes on the safety and effectiveness of the diet, but what they seem to agree on is that it’s not one-size-fits-all.

 

OMAD diet and weight loss

 

The OMAD diet promotes weight loss primarily through calorie restriction. With one meal a day, people have limited time and space to consume their daily calories. This can lead to weight loss for some people, but whether or not it leads to healthy weight loss isn’t so definitive.

While some studies have found eating one meal a day to promote weight loss and reduced body fat, studies have also found the diet can induce higher blood pressure, higher HDL and LDL cholesterol, increased hunger, and decreased fullness, among other negative impacts. Researchers also note that more research is needed to confirm the positive or negative impacts of extreme fasting.

Meessen EC, 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;12. doi:10.3389/fphys.2021.771944

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;85(4):981-988. doi:10.1093/ajcn/85.4.981

 

“People on the OMAD can end up losing weight, but it is all about consistency and doing something long-term for its full effects and benefits,” says Amy Lee, MD, Head of Nutrition for Nucific. Lee recommends the OMAD diet for clients who need to lose weight and struggle with fixations about meal timing.

“Not having to eat multiple times a day can eliminate the stress of having to think about food,” Lee says. “Some people struggle having to make decisions regarding prepping and timing of eating.”

She adds that some people may undergo the diet for religious purposes, too. In all cases, people who only eat one meal a day must be vigilant at properly nourishing themselves during their allotted time frame, she says. This can mean striking a balance between not gorging themselves to the point of bloating and not missing out on key nutrients, either.

“If a patient decides to undergo the OMAD, then it would be a good idea to actually map out what foods and drinks should be taken in and make sure their daily essential vitamins, minerals, and amino acids are taken into consideration,” says Lee. 

Yet, rather than rely on supplementation, people could replenish missing nutrients by eating another meal—or even meals—a day.

“From a nutritional perspective, I wouldn't note any benefits,” Christyna Johnson, MS, RDN, LD, dietitian and founder of Encouraging Nutrition, LLC, says of OMAD. “This significantly limits the nutritional adequacy and variety someone can consume.”

Johnson does not recommend this diet to her clients due to the risks involved and the slippery slope to malnutrition. If clients come to her and express interest in the diet, she says that she tries to understand what draws them to the trend first, and then figures out how to best support a healthy alternative. She encourages doctors to do the same.

“For doctors who encounter patients who are following OMAD, ask the patient, Why are [you] choosing to follow this? What are [you] hoping will come from following OMAD?” Johnson says.

Motivation may help gauge what type of physical or mental health state the patient is coming from. “Typically, people who are already restricting meals during the day are drawn to OMAD,” Johnson says. “Those who are less aware of their cues for physical hunger will lean into this way of thinking.”

She recommends referring the patient to a dietitian who can provide individualized nutrition advice and care that fits their needs and goals.

Lee also stresses that not everyone is fit for the OMAD diet and that it can pose risks to metabolism function or insulin management and for dehydration and malnutrition. 

 

OMAD diet and metabolism

 

Since most people get hungry more than once a day, the OMAD diet encourages ignoring bodily hunger queues, which can be disruptive to metabolism. This may be disruptive, as hunger recognition helps regulate energy levels and immune function, according to studies.

Milazzo N, OMAD And 20:4 Intermittent Fasting. Examine. September 28, 2022. (discusses increased hunger)

Ciampolini M, Lovell-Smith, Bianchi, Kenealy T. Hunger can be taught: Hunger recognition regulates eating and improves energy balance. International Journal of General Medicine. Published online 2013:465. doi:10.2147/ijgm.s40655

 

This is also one of the reasons the diet is hard to maintain and not healthy for everyone. “The brain will fight you and remind you that you need fuel throughout the day,” says Lee.

For people with conditions like diabetes, it can also disrupt insulin management. Lee does not recommend OMAD for people with diabetes or other metabolic conditions.

Johnson adds that some of the negative side effects from OMAD can start to come up early on in the dieting process, particularly if people are not eating enough for their one meal. These can include irritability and brain fog, which can be a result of hunger and/or lack of nutrition.  

Longer-term consequences can include a slowed metabolism; feeling cold when others are not; changes in hair, skin, or nails; and feeling lightheaded or dizzy, she says. Constipation can also be a side effect of malnutrition.