The "One Meal a Day" diet, or OMAD, is an extreme form of intermittent fasting that involves consuming all of your daily calories in a single meal within a one-hour window and fasting for the remaining 23 hours. Proponents claim it promotes weight loss by forcing the body to burn fat. Like other kinds of intermittent fasting, eating one meal a day manipulates how your body finds and uses fuel.
How the OMAD Diet Works
When you eat in a traditional pattern, your energy comes from the food you eat. When you take in carbohydrates, your body breaks them down into sugars. If you have more sugar in your blood than you need, a chemical called insulin will carry the extra into your fat cells. When you don’t eat for extended periods of time, your body produces less insulin. Your cells still need energy for fuel, so your fat cells release energy to compensate. For this to happen, however, you have to avoid eating for long enough that your insulin levels drop.
Potential Benefits of the OMAD Diet
Research on intermittent fasting is promising. The OMAD diet may help some people achieve their weight loss goals.
- Weight Loss: Eating just one meal a day reduces calorie intake compared to consuming three meals, leading to effective and rapid weight loss. Study participants who tried eating one meal a day ended up with less total body fat. Intermittent fasting, in general, has proven to be an effective weight-loss method. The typical weight loss is 7 to 11 pounds over 10 weeks. Eucaloric meal reduction to a single meal per day lowered total body mass and fat mass.
- Improved Metabolism: In adult men with prediabetes and obesity, a 6-hour period of eating followed by 18 hours of fasting improved their blood sugar levels. It's worth noting that these men followed a more general time-restricted eating plan, and not a strict OMAD diet. More research would be necessary to know whether eating one meal a day has the same effect.
- Increased Alertness: When you fast during daylight hours, your body releases more of a chemical called orexin-A, which makes you feel more alert. This also isn’t specific to OMAD, and it wouldn’t apply if you ate your single meal in the morning.
- Simplified Meal Planning: With OMAD, there is no need to plan multiple meals throughout the day.
- Increased Concentration and Productivity: Since the one-meal-a-day diet does not include lunch, it can eliminate the sluggishness of the body when digesting food for lunch.
Risks and Drawbacks of the OMAD Diet
The OMAD diet is a restrictive eating approach that won’t necessarily appeal to everyone. It is strict, and there’s no conclusive evidence that eating one meal a day works for weight control. Whether it’s worth the discomfort depends on your tolerance and body chemistry.
- Difficulty Sustaining: Intermittent fasting regimens like OMAD have a dropout rate of up to 65%. It’s no easier to follow than other calorie restriction plans.
- Increased Hunger: When you eat one meal a day rather than three, your body produces more of a hormone called ghrelin, which makes you feel hungry.
- Potential for Overeating: If you’re following OMAD, you’ll need to take care not to overeat or overindulge on unhealthy foods during your main meal. You may also struggle to fit an entire day’s caloric intake into one large meal - or find yourself feeling uncomfortably full after eating this much in one sitting.
- Nutrient Deficiencies: Eating one meal a day is unlikely to give you the calories and nutrients your body needs to thrive unless carefully planned. It can be very difficult to take in enough nutrients in one meal. This can lead to nutrient deficiencies, which can negatively affect your health and can lead to serious risks.
- May Not Be More Effective Than Calorie Reduction: Even if the OMAD diet makes you feel hungrier, it’s unlikely to lead to more weight loss than if you simply reduced the number of calories you took in during the day.
- Increased Blood Pressure and Cholesterol: Eating one meal a day can increase your blood pressure and cholesterol. This occurred in a group of healthy adults who switched to one meal a day to participate in a study. If you already have concerns in either area, eating just once a day might not be safe.
- Blood Sugar Spikes and Crashes: Eating one meal late can cause your blood sugar to spike. These participants had morning blood sugar levels that were higher than normal, and their bodies were less able to deal with this extra sugar. Fasting can cause blood sugar crashes. Fasting of any type increases the risk of extremely low blood sugar, also known as hypoglycemia, in people who have Type 2 diabetes.
- Other Potential Risks: Shakiness or physical weakness, Intense hunger or binge eating, Fatigue and low energy levels, Brain fog or difficulty concentrating.
- Not Suitable for Everyone: The OMAD diet can be extremely dangerous for children and young adults who are hypoglycemic, have diabetes, obesity, or metabolic disorders. Moreover, this diet can also increase the risk of binge eating. Another word of caution: If you take medication that must be consumed with food, reconsider OMAD. Not taking meds as prescribed could negatively affect absorbability and increase your risk of side effects. Shapiro also advises that people living with diabetes who are taking insulin should not follow this diet, as OMAD can affect blood sugar levels. Finally, if you often have gastrointestinal (GI) issues like bloating or an upset stomach, OMAD may not be a good fit for you.
Who Should Avoid the OMAD Diet?
For most people, there are no serious dangers involved in eating one meal a day, other than the discomforts of feeling hungry. That said, there are some risks for people with cardiovascular disease or diabetes.
Read also: One Meal a Day Keto
OMAD may actually be unsafe for certain groups of people. This includes people who are pregnant or nursing, who are younger than 18, and people who have an eating disorder or a history of disordered eating. In general, people with diabetes need to eat balanced meals regularly throughout the day. Going prolonged periods of time without eating can lead to harmful blood sugar lows followed by subsequent highs once a larger meal is inevitably consumed. This pattern of inconsistent eating can make it difficult to keep blood sugar levels low and stable.
How to Apply the OMAD Diet Safely
The safety and effectiveness of any weight-loss plan are unique to each person. The "one meal a day" diet, also known as OMAD, can offer potential health benefits such as weight loss and disease prevention if implemented correctly. However, this eating style is not suitable for everyone. Before starting any diet plan, you should consult with a nutrition expert for guidance.
If you are interested in trying OMAD but have not yet tried other types of IF, start slowly. Start with a 12-hour fast and then build up to 14 or 16 hours. If you’re going to attempt it, you still have to make sure you’re doing your best to eat balanced and nutritious meals and that you’re still eating enough calories for the day if you want to stay healthy. Fasting alone won’t be beneficial if [you’re] not carefully constructing the meals you’re eating in that time frame.
- Consult a Healthcare Professional: Always speak to your doctor or an RDN before starting a new diet, especially if you’re managing an underlying health condition or taking medication, or if OMAD represents a dramatic change in the way you eat. To determine whether OMAD is suitable for you, consult a nutritionist for advice.
- Start Slowly: If you are interested in trying OMAD but have not yet tried other types of IF, start slowly. Start with a 12-hour fast and then build up to 14 or 16 hours.
- Focus on Nutrient-Dense Foods: If you do choose this eating pattern, it’s essential to ensure that you’re consuming a variety of nutritious foods, including: fruits, vegetables, starchy vegetables and grains, healthful fats, legumes, seeds, nuts, and nut butters, dairy and plant-based alternative products, protein sources. Limit highly processed foods, such as: fast food sugary baked goods white bread sugary cereals soda chips.
- Stay Hydrated: During fasting windows, the OMAD diet requires people to keep calorie intake to a minimum. In the strict OMAD diet, this means complete restriction of calories. You can still enjoy water and other noncaloric beverages during fasting periods. Others choose to eat low calorie, high protein snacks during the day, such as: egg whites chicken tuna
- Listen to Your Body: The key to success with OMAD-or any diet-is listening to your body. If OMAD causes severe negative effects on your health, discontinue the diet and opt for a more suitable approach.
What to Eat on the OMAD Diet
There are several versions of the OMAD diet. Some suggest eating healthful, nutrient-rich foods, but most allow people to eat anything they want.
People who follow the OMAD diet believe that it offers numerous benefits, such as: rapid weight loss, no calorie-counting, it does not exclude any foods.
Read also: Combining Keto and OMAD
If eating one meal a day, try to make meals as nutrient-dense as possible. These meals should deliver at least 1,200 calories, which can be difficult for some to ingest over a typical meal window. If you find it challenging to eat enough calories in one meal, consider increasing your eating window by an hour or so and splitting your meal into two smaller meals. This can help you get enough nutrients and calories without becoming overly full.
Here are some nutritionally complete meal ideas that are likely to exceed 1,200 calories if portion sizes are large enough:
- Baked chicken with mashed sweet potatoes topped with butter and roasted broccoli with olive oil, followed by full fat Greek yogurt topped with berries, nuts, seeds, and honey.
- Grilled salmon topped with guacamole, brown rice and black bean salad, and roasted plantains, followed by fruit served with nut butter, hemp seeds, and coconut flakes.
- Egg omelet with goat cheese, avocado, and grilled vegetables cooked in coconut oil, crispy baked potato wedges, followed by a side of fruit dipped in dark chocolate and whipped cream.
As you can see, each meal should account for all food groups and include: carbohydrates fats proteins In a day, eating 1,200 calories is a general minimum. Most adults need much more than that to maintain their weight.
Keep in mind that this way of eating is much more difficult for those following specific dietary patterns like vegan diets or low fat diets due to the number of calories that must fit into a single meal. Overall, trying to cram all your calorie needs into one meal is not necessary no matter what your health goal is. This dietary pattern is also not sustainable or practical for most people.
The Best Time to Eat During OMAD
Research from 2020 suggests that eating later in the day is associated with cardiometabolic risk and less success with weight loss than eating earlier. Therefore, a person may want to try eating earlier in the day. However, no research compares how different meal times may affect the results of the OMAD diet.
Read also: Beginner's Guide to OMAD
Eating in the morning and fasting overnight can help you lose weight. The OMAD diet doesn’t tell you which meal to eat. That said, people who fast overnight and eat a larger meal in the morning tend to lose more weight than people who eat more at dinnertime.
Why You May Not Be Losing Weight on OMAD
People may not lose weight while on an OMAD diet for a number of reasons. For example, they may be overeating during their single meal time. Alternatively, individual differences in metabolism and other factors can make weight loss more difficult for some people.
If you are eating only one meal a day, you may find yourself overeating during your one meal if you are not mindful of your food intake. It’s important that your one meal is particularly balanced. With an increase in hunger, the temptation to overly eat highly processed, high carb foods may be harder to resist, leading to a net increase in calories, especially if you are not staying physically active.
Alternatives to the OMAD Diet
If you want to try fasting but are unsure about OMAD, consider a more manageable approach, like the 5:2 diet or the Warrior Diet. Those interested in fasting should consider less restrictive forms of fasting. More sustainable eating plans include 16/8 intermittent fasting or simply following a healthful, lower calorie dietary plan if you’re currently eating in a surplus and want to promote weight loss.
As well as adopting a nutritious, balanced diet, a person may also wish to consider the following: eating smaller but more frequent meals, reducing evening snacking, exercising regularly, keeping a food diary, getting support from a healthcare professional, such as a dietitian, loved ones, or weight loss support group.