Three weeks ago I wrote about how, after reaching my heaviest body weight ever, I had finally had enough and would try dieting and lifestyle changes in an attempt to get back to my high school weight. I wrote how I didn’t really start with a plan other than to not eat unless I was actually hungry, and how this naturally led me to practice OMAD (i.e. one meal a day)—something I had never done before since my life was always fairly regimented and social, and most families eat multiple meals per day.

I ended up settling on eating around noon, and what surprised me most about eating only one meal a day was how little hunger I actually felt in the evening and morning, only feeling small cravings sometimes in the evening that quickly disappeared by drinking water and doing something else, like going for a walk. Even when noon came around the next day, I still didn’t feel famished, by any means, but I still cooked myself a healthy meal and followed it up with a cup of iced milk coffee.

Despite never feeling unbearably hungry, I was pleased to see that, unlike other dieting attempts I had made in the past, I was seeing significant results and seeing them quite quickly, which motivated me to continue practicing OMAD for what has now been four straight weeks. In this time I lost 9 pounds the first week, another 5 pounds the second week, another 4 pounds the third week, and 2 more pounds the fourth week—a total of 20 pounds in one month despite being only 30 pounds over my high school body weight!

During these past four weeks I also increased my time exercising, but nothing drastic. Before this, outside of normal everyday activity (which, admittedly, wasn’t much given my desk job), I usually went jogging about 10 miles per week, lifted weights once a week, and walked for 30 minutes per day. I’ve since upped that to about 15 miles of jogging per week, lifted weights still once a week but with an added set for each lift, and 60 minutes of walking a day, none of which has been strenuous.

As evident by the approximate halving of my weight loss each week as I come closer to my target weight, while I’m still continuing with OMAD for now, I expect it will take longer to shed these final 10 pounds than it did to shed the first 20. However, its impressive efficacy so far made me wonder why it worked so well, so quickly.

It turns out that OMAD is simply one of the stricter routines for intermittent fasting (also known as “time-restricted eating”), tagged as a 23:1 routine where one fasts for 23 hours and then eats during a 1-hour window. More liberal intermitting fasting routines include an 18:6 routine, where one fasts for 18 hours but then eats within a 6-hour window (e.g. skip breakfast, eat lunch at noon and then eat dinner at five o’clock, and perhaps even snacking in between). Or, if that’s too difficult still, some intermittent fasters may try a 16:8, allowing them to spread out their meals, snacks, and non-water drinks across 8 hours.

Despite longer eating windows for the latter intermittent fasting routines, the idea is still to achieve caloric deficiency. However, as I looked into why the 23:1 routine (i.e. OMAD) was working so well, I learned why less stringent routines might be less effective: it’s not just about calories in versus calories out but also about how the human body works in digesting food.

Indeed, one of the biggest reasons why intermittent fasting works is that by reducing the eating window you’re less likely to overfeed yourself: even as studies show that intermittent fasters tend to eat larger meal portions than non-fasters, they still end up eating fewer calories overall. It turns out, people are generally pretty bad at estimating the number of calories in their meals, and almost always end up underestimating things. Fewer opportunities to overeat mitigates that (admittedly, so would strict, methodical calorie counting, but that can be exhausting, off putting, and unrealistic for many).

The second big reason why intermittent fasting works, though, is the reason why 23:1 is more effective than 18:6 or 16:8. In short, it keeps insulin levels low, which forces our bodies to start burning stored fat instead. The longer we fast, then, the longer our body is in fat-burning mode. This excerpt from a Harvard Health article explains it well:

“[Intermittent fasting] makes intuitive sense. The food we eat is broken down by enzymes in our gut and eventually ends up as molecules in our bloodstream. Carbohydrates, particularly sugars and refined grains (think white flours and rice), are quickly broken down into sugar, which our cells use for energy. If our cells don't use it all, we store it in our fat cells as, well, fat. But sugar can only enter our cells with insulin, a hormone made in the pancreas. Insulin brings sugar into the fat cells and keeps it there.

“Between meals, as long as we don't snack, our insulin levels will go down and our fat cells can then release their stored sugar, to be used as energy. We lose weight if we let our insulin levels go down. The entire idea of IF is to allow the insulin levels to go down far enough and for long enough that we burn off our fat.” -- Harvard Health Publishing Staff (February 28, 2021)

Reading this immediately made me think of the “feast or famine” phrase used to describe the lifestyles of our ancient ancestors. Only in comparably recent times have humans been blessed with an abundance of food, consistently supplied. Eating constantly and at our leisure is a modern phenomenon. In fact, the Harvard Health article touches on this as well: “Fasting is evolutionarily embedded within our physiology, triggering several essential cellular functions. Flipping the switch from a fed to fasting state does more than help us burn calories and lose weight.” Consequently, they conclude that fasting “improves metabolism, lowers blood sugar levels; lessens inflammation, which improves a range of health issues from arthritic pain to asthma; and even helps clear out toxins and damaged cells, which lowers risk for cancer and enhances brain function.”

Thus, the benefit of avoiding calories during the fasting window is how it ties into the release of insulin. Except it’s not just about avoiding calories, as even artificially sweetened, calorie-free drinks can trick the brain into thinking you are hungry, as noted by clinical specialist, Dr. Morgan Nolte, paraphrased here:

“Sugary beverages, alcohol, and many zero or low calorie drinks like ice, Coke Zero, really anything sweet, will trigger the hypothalamic region in your brain to make you think that calories are coming in. The hypothalamus then sends a signal to your pancreas via your vagal nerve that says, 'Hey, you better get some insulin pumped out because we have some sweet stuff coming in.' Then the insulin gets pumped out, but there's not really a direct rise in the glucose because you didn't actually eat any sugar or calories. So insulin pushes glucose already in your bloodstream into your cells, which lowers blood sugar. This drop in blood sugar sends a signal to your brain to increase your hunger, which is not something that we wanna do when we're fasting [sic]” -- Leah Groth (July 16, 2024).

When I read that, I thought of the famous Donald Trump tweet about Diet Coke: “I have never seen a thin person drinking Diet Coke.” -- @realDonaldTrump (October 14, 2012).

Of course, I haven’t just been intermittent fasting and exercising more, I’ve also been eating more healthily overall, cutting out added sugars entirely (still eating natural sugars such as those found in dairy, though) and severely limiting processed foods and those cooked in unhealthy oils (in fact, pretty much the only processed food I’ve been eating are tortilla chips [corn, oil, salt]). And I’ve been sure to avoid eating or drinking anything (besides water) during my fasting window—even Diet Coke.