The “One Meal a Day” diet, or OMAD diet, claims to help you lose weight by forcing your body to burn fat. It’s a type of intermittent fasting, which alternates between periods throughout the day in which you can eat anything and periods in which you don’t eat at all.
OMAD is particularly strict because you don’t eat for 23 hours, then consume all of your calories in a single meal.
How It Works
Like other kinds of intermittent fasting, eating one meal a day is a way of manipulating how your body finds and uses fuel. When you eat in a more traditional pattern, your energy comes from the food that 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.
The Pros
Research on intermittent fasting is promising. The OMAD diet isn’t a magic bullet, but it may help some people to achieve their weight loss goals.
It may help you to burn fat. Study participants who tried eating one meal a day ended up with less total body fat. This particular group of people didn’t experience significant weight loss.
That said, 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.
It can improve your 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.
You could feel more alert. 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.
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.
The Cons
This diet 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.
It can be difficult to sustain. Intermittent fasting regimens like OMAD have a dropout rate of up to 65%. It’s no easier to follow than other calorie restriction plans.
It may make you hungrier. When you eat one meal a day rather than three, your body produces more of a hormone called ghrelin, which makes you feel hungry.
It’s no 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.
Safety Concerns
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.
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.
Eating one meal late can cause your blood sugar to spike. Some OMAD studies have asked people to eat their single meal between 4 p.m. and 8 p.m. 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.
The safety and effectiveness of any weight-loss plan are unique to each person. It’s best to speak with a doctor one-on-one if you have questions or concerns about trying the "One Meal a Day" diet plan.
