Biology question

I was discussing IF recently with a friend. He acknowledged the scientific evidence for many health benefits of IF. However, when it comes to weight loss, he claimed that any weight loss during IF is entirely attributed to the fact that most IF'ers consume fewer calories than they otherwise would. He went a step further and claimed that there is scientific evidence for this. (I didn't press him on providing it.) Is this true? I thought that there was evidence for weight loss due to the lower insulin levels alone, and if a person eats the same number of calories per day on or off IF, they'd still be more likely to lose weight on IF than they would without it. However, I couldn't remember where I heard/read this, so I wasn't really prepared to argue it.

Answer

Agree with your friend. There is some research about the insulin side, but ultimately its CICO. If you eat at or above your TDEE, you’ll stay the same or gain, no matter how short your window is.

For 99% of people, it’ll always be about the math….gotta burn more than you consume!

Answer

Some studies suggest that IF outperforms traditional (continuous) energy restriction, others report a tie between the two. Insulin sensitivity may be a reason for this discrepancy: Someone operating at the pinnacle of metabolic health already may not benefit from IF nearly as much as a type 2 diabetic, whose energy expenditure is significantly compromised by hyperinsulinemia.

Regardless, the question is what matters most, the ability to effortlessly avoid excessive intake or increase one’s expenditure. My take would be that the former is always more important, simply because of magnitude – no metabolic edge is powerful enough to negate the wrong food choices. The most promising studies out there report “gains” in expenditure thanks to IF on the order of a few hundred calories a day at best; impressive no doubt, but then again trivially undone.

In pre-OMAD times I would sip a liter or so of fruit juice a day; possibly wander into the kitchen half a dozen times for something like a handful of nuts or a slice of cheese while in a mindless distraction-seeking state; devour a family-sized pizza worth how many thousand calories lord only knows every Sunday; munch on stuff while stuck in traffic; accompany my beverage at a café with a sandwich or sweet; relax over a glass of scotch in the evenings. Compare the efficacy in cutting all that out without feeling miserable against the 200-something calories by which OMAD may be boosting my daily expenditure; I’m very grateful for the latter bonus, if I am in fact receiving it, but it’s not the decisive criterion for my choice of protocol.

Answer

Calorie deficit, that is all. When what you consume is less than what you ‘use up’. IF is a method to consume less by reducing your feeding window. James Smith is the no BS ‘Calorie F*cking Deficit Guy’ if you want to find a more scientific explanation on Instagram or YouTube.

It goes for any diet that helps with fat loss, it just puts you in a Calorie Deficit, that’s why low carb diets work so well because how much food has carbs in it? Loaaaaads. Cut out all foods with carbs and you don’t have much left e.g no pasta, bread, cereal, potatoes, rice, chocolate etc etc. so overall you consume less of these high carb/calorie dense foods.