If I understand correctly, most of these fasts seem to work by rapidly emptying out your water weight. You might lose 10 lbs quickly and see your belly flatten, but it's not 10 lbs of fat. It might be a pound or two of fat, a disproportionately high percentage of muscle because you're not feeding your body, and dumping out your sodium and glycogen, both of which help you retain a lot of water. Losing that water weight will help you in much the same way that a bodybuilder will dehydrate themselves before a competition - you'll see your skin become less puffy and some muscles will be visible that previously weren't. And that isnt necessarily a bad thing - it might be motivation to lose the next 8 or 9 lbs of actual fat.
But if you just do the fast and lose ten lbs, then return to your normal eating habits, your experience will most likely be that the weight seems to come back quickly, and if you don't expect it, you might start to question your metabolism or your body's ability to lose those ten lbs.
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So I wrote that without reading the article, then read it to make sure I was being fair. I think I was. If you read the article, he makes a big deal about losing 15 lbs quickly and then needing to keep it off... that's almost certainly because some people experience what I just described. The keeping it off part is just hand waving around an actual diet - keep it off by starting to eat healthy foods. That’s not unique to fasting, it's just how dieting works, you usually lose a bunch of water weight early and then keep it off until you stop dieting. Check the lets lose some weight in 2021 thread and you'll see tons of people charting their weight loss with drops of 5 lbs in the first week and 10 by the end of week 2.
The article then points out that Mickelson lost 15 lbs the first week and another 15 the next few months. What really happened is probably that he lost his water weight quickly, lost 15 lbs of actual fat by actually dieting, and then put the water weight back on at the end but didn't mention it. 15 lbs in a few months is a pretty normal, sustainable pace with a simple diet like he described that isn't calorie restricted.
I get that it's a fun article in golf digest, and i always thought it would be fun to try this, long before Vivian darkbloom graced us with the grizzly details of non-golf digestion, but I wouldn't recommend it. If you do this, though, I would recommend taking a before and after picture of your abs because they'll probably look the best they've looked in years but not for very long.
I am not a doctor and this is not medical advice. Consult your doctor before beginning this or any diet or exercise program.