Theres been recent studies showing that Fasting is no better than other forms of weightloss in terms of how much weight is lost for a given calorie deficit. By just reading the ‘headline’ result, many people are left wondering why use fasting for weightloss at all then? Well for a myriad of reasons!!
Lets talk about the downsides of Conventional CICO diets first. Usually these follow the S.A.D. (Standard American diet) of 3 meals a day plus several snacks….just calorie reduced versions. This means none of the meals or snacks are very satiating and one can be constantly hungry and feeling deprived. If you run too high of a calorie deficit eating this way you will constantly plateau and then YoYo regain the weight at the end because you crashed your metabolism. The reason is that eating that often spread across the whole day keeps your insulin levels raised most of the day. Insulin is the Fat storage hormone and you can only store fat not access and burn it with insulin in the blood. Your body doesn’t have enough insulin free hours in the day to burn enough fat to make up for the large dietary calorie deficit and so it has no choice but to lower your metabolism instead. As your crashing metabolism catches up with your diet intake you plateau. You cut calories even more or exercise more to restart weightloss, but your metabolism resumes the chase. You either reach goal weight or give up the diet. you don’t even go back to old bad habits but start eating what should be your new maintenance calories at your new weight….and you start rapidly regaining weight. This is because what should be your new maintenance is actually a large surplus relative to your crashed metabolism. As you regain the weight your metabolism recovers but you are back to where you started. You summon the motivation to start again but use the same diet plan again. The exact same thing happens and new you know what YoYo dieting is.
The main reason the recommended daily calorie deficit is only 500kcals a day is that this is close to what your metabolism would drop to simply due to the weightloss where it takes less calories to maintain and move a lighter body around. For example, My TDEE (Total Daily Energy Expenditure = BMR + Avg Daily activity = Maintenance calories) was 2400kcals at 200lb but will be 2050kcals at my goal weight of 145lb. So even if I ‘Crashed’ my metabolism with a conventional CICO diet, if my daily deficit was only 500kcals then I haven’t crashed it much beyond what it would have fallen to anyway at my goal weight.
The problem with a 500kcal per day deficit is that it means only 1LB a week of fat loss. This glacial rate of fat loss is easily potentially swamped and hidden for weeks simply due to Glycogen Water, Poop, Electrolyte water, Menstrual cycle fluid retention variability. So folks are hungry all the time on this kind of diet and yet they see virtually no progress for weeks on end and sometimes it even looks like they are going backwards because for example 3 weeks worth of fat loss was masked by as little as 1.5L of water retention…or constipation!! LOL No wonder so many throw in the towel on diets so quickly so often!! They either run a high enough deficit to see enough progress that keeps them motivated longer but end up crashing their metabolism and inevitably regaining or they run the recommended daily deficit, don’t crash their metabolism but see such slow progress they never lose much weight before giving up in frustration anyway.
Intermittent and extended fasting on the other hand you can run much larger deficits without crashing your metabolism because you’ve left more than enough insulin free hours in the day for the body to access and burn all the calories it needs to make up for the dietary calorie deficit and thus your body has no need to crash your metabolism. The real magic of IF/EF IMHO is in its Ghrelin Hunger Hormone suppression. Your body quickly learns to secrete this hormone at your regular mealtimes to remind you to eat with psychosomatic effects like hangriness, lethargy, jelly legs etc which people assume is low blood sugar or hypoglycemia but isn’t. If it was it wouldn’t just disappear as if by magic about the 2 hour mark when the Ghrelin surge subsides. If you skip a meal or meals only a few days in a row you deprogram that Ghrelin surge and as long as you didn’t move those calories to the remaining meals, you created a calorie deficit without having to be obsessive about calorie counting. With the Ghrelin surge deprogramed you don’t even feel hungry at or miss the old mealtimes. You still get to eat the same delicious food and portion sizes you always ate for the remaining meals so don’t feel like you are depriving yourself of anything. This is why IF can be so easy and so sustainable to do over the long term of weeks, months and years. The likes of Ozempic/Wegovy are leveraging a different hormonal pathway to suppress appetite and cravings and it frustrates me that folks are paying hundreds a month for those drugs when they could leverage their own Ghrelin Hunger Hormone for free with the same or even better results with IF.
So given the same macros, nutrients and calorie deficit, will you lose any more weight with Fasting? No. Will you be able to run much larger calorie deficits though without risk of crashing your metabolism for much faster weightloss and will you be able to keep the fasting ‘diet’ going much much longer because there is no constant hunger or sense of depriving yourself of anything. Yes.
So Calories in and Calories Out still matter even with fasting, but thats only half the story. The weightloss is coming from the Calorie deficit but that calorie deficit was able to be larger, was made easy to create and easy to sustain by the tighter eating windows and its effects on several of your hormones like Insulin and Ghrelin. Haven’t even mentioned IF’s tigher eating windows ability to cure any insulin resistance, metabolic syndrome or pre-diabetes you may already have developed, nor have I mentioned the inflammation reduction from gut rest, reseting the gut biome to a healthier ratio of good bacteria or the myriad benefits of fasting induced autophagy.
Put simply, IF is probably the fastest, easiest, most sustainable and most metabolically healthy way to lose and then maintain weight.
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