One meal a day or "OMAD" is another form of intermittent fasting. After 16hrs of fasting, your body gets more and more into fat burning mode or "ketosis", where the body uses fat rather than glucose for energy production. If you want to understand the chemical details of it, I recommend you have a look at Dave Asprey's "Fast this way" pg. 70ff. Your basal metabolic rate becomes more efficient, your heart rate and blood pressure will lower. Some studies have found other beneficial effects such as lower triglycerides ("bad fats") and higher high density cholesterol (HDL, the "good stuff", which is used for cell membranes and hormone production). After 24 hrs of fasting you are in full "ketosis".

Fasting for more than 17hrs also triggers the process of "autophagy", where the body uses a series of bimolecular tools to "clean" the body from cells and cell parts it no longer needs. Various studies (on mice!) suggest that autophagy slows the aging process, reduces inflammation and enhances the body's performance. It's also suggested that fasting has a positive influence on another anti-aging molecule called NAD+ (nicotinamide adenine dinucleotide), which plays an important  role in energy production in the cells. Another study by MIT found that fasting for 24 hrs improves stems cell production in the gut, as well as the composition of your microbiome in a positive way. 

So, how to do it? It's totally up to you whether you'd like to try dinner to dinner, lunch to lunch, breakfast to breakfast! If you do this once, try to really stick to a 24 hrs pause, so you get all the benefits of the 24 hrs fast. What should you eat, when you eat? Dr Mindy Pelz recommends 50 gr net carbs and 60% of calories from fat. Now, I know, that is really hard. So for starters, you might just want to eat much less carbs than you usually would, avoiding your pasta, potatoes, bread, and really try to add some extra olive oil, butter or coconut oil to your meal before you stop eating for 24 hrs. 

Again, opinions differ on whether your should basically be eating one meal a day always, or whether you should alternate different forms of fasting with periods of eating. Personally, I'm more on the side of people like Dave Asprey and Mindy Pelz, who suggest to alternate between different types of fasting and non-fasting phases - as Dave says: there is fasting and starving. You want to avoid the latter. Fasting too much could have a negative consequence on your sex hormones and your sleep, trigger hair loss, etc.

Again, listen to your own body, if you're a pre-menopausal women, observe your cycle and try different fasts, diets and feasts (!) depending our your life style and your physical condition.

If you want to try OMAD check out another one of Dr. Mindy Pelz' easy to understand, super informative videos:

If you want to go deeper into the science, get Dave Asprey's " Fast this way".