The Trendy OMAD Diet Has a Ton of Potentially Scary Side Effects (2024)

The one meal a day (OMAD) diet is, simply put, fasting from food for 23 hours a day and eating whatever you’d like for one meal. That meal can range from a double cheeseburger and fries to a more healthful salad loaded with greens, roasted veggies, whole grains, beans, nuts, and seeds. The idea is by limiting your calorie consumption throughout the day, you can feast on one meal (usually defined as a one-hour window) and still lose weight.

Water and unsweetened coffee and tea are allowed, but otherwise, the kitchen is closed — all day long.

Is the OMAD diet the same as intermittent fasting?

The one meal a day diet is a type of time-restricted intermittent fasting, in which dieters will fast for 12 or more hours per day. In this case, of course, it’s 23. Most people do this by starting a fast at night, skipping breakfast, and eating their first meal in the middle of the day — with another seven hours or so left to fantasize about food before going to bed.

The one meal a day diet is so extreme it makes the other versions of fasting look tame. With the 16:8 diet, for example, you can eat during an eight-hour window (like between 9 a.m. and 5 p.m.) and fast for the other 16.

Alternate day fasting, also known as the 5:2 diet, has you limiting your calorie intake a couple days each week and then eating regular meals and snacks on the days in between.

Can you lose weight by eating one meal a day?

When you’re only eating one meal per day, you’re likely consuming a significantly fewer amount of calories than you normally would. Reduced calorie consumption usually results in weight loss; larger-scale studies have found that people who practiced fasting and people who simply decreased calorie intake overall lost the same amount of weight.

It’s very easy to feel deprived when practicing the OMAD diet, which could lead to binging and falling off the wagon. Prolonged periods of restriction often beget weight cycling (i.e., "yo-yo-dieting") and changes to your hunger hormones and metabolism. Ultimately, you may feel hungrier after trying the one meal a day diet than you might’ve felt before you started this restrictive plan. To make food choices that ultimately lead to better health and subsequent weight loss, it’s not feasible for many of us to simply restrict food entirely for set periods of time.

Is the OMAD diet healthy?

The idea behind intermittent fasting is that its gives your vital organs, digestive hormones, and metabolic functions a "break" and reduces oxidative stress on the body. Proponents believe reducing stress via fasting improves the function of your organ tissues, reduces inflammation, and lowers your risk for chronic disease. It’s also credited with reducing susceptibility to insulin resistance, which could lower your risk for diabetes.

However, there’s substantial evidence suggesting that any benefit is quickly undone as soon as you break the fast, causing the appetite-suppressing hormones to switch gears and make you feel even hungrier than you felt at baseline.

A real potential benefit of time-restricted fasting is that it could help you go to bed earlier — a very crucial component to any weight loss plan. Getting seven hours of sleep per night as been linked to weight management, reduced risk of chronic disease, and improved metabolic benefits.

Is the OMAD diet bad for you?

There’s very little scientific data supporting the one meal a day diet, which is scarily similar to a disordered eating practice. There are some major risks and potential negative consequences associated with this type of pattern:

• You're ignoring your body's own hunger cues. If you’ve only got one hour out of the day to consume nutrients, it’s highly likely that you’re going to eat as much as you possibly can, which isn’t exactly priming your body and intuition to understand when you feel full or hungry.
  
• You could miss out on important nutrients. In order to get enough key antioxidants, minerals, and phytonutrients, you’d have to pack in five daily servings of veggies and fruit, not to mention whole grains, legumes, nuts, seeds, lean protein, and some dairy products (or dairy alternatives) in that one-hour window.
• Your bad cholesterol levels could go up. Fasting has been linked to increases in LDL cholesterol, which is basically the opposite of what you’re trying to achieve!
• You could slow your metabolism. The more you restrict, the slower your metabolism becomes as a response. That can lead to unwanted side effects in the long run, including weight gain.
  

What happens if you only eat one meal a day?

The side effects of restricting food for nearly an entire day can include:

• Lightheadedness
• Nausea
• Blood pressure destabilization
• Dizziness
• Confusion
• Hypoglycemia (low blood sugar)
• Dehydration

Consider what else might happen by eating one meal per day. It's hard to exercise regularly (another important factor to your health) when you're not fueled appropriately. You could miss out on various experiences and meals shared with family and friends. Plus, you're following rules instead of making choices. That's the opposite of cultivating a mindful eating practice, which could majorly backfire when you decide to go off of this plan.

The Bottom Line

If you still want to try the OMAD diet, strive for a wide variety of nutrient-rich foods like fruits, veggies, whole grains, and lean proteins. Do not try this type of plan if you’re pregnant, lactating, or taking medication that requires food for metabolism of the drug. Even if you don't experience any short-term side effects, studies have yet to find out how fasting can affect humans in the long run.

Instead, I'd encourage you to keep it as simple as possible: Experiment with an "early bird special" for dinner; close your kitchen once you’re finished; aim to get more sleep overnight, and sit down for a full breakfast at your usual time tomorrow.