[dlytle]

One of the primary arguments of a keto/paleo diet is that the different diets affect how many calories your body thinks it needs, how it uses them, and how it influences behavior as a result. (Disclaimer: using imaginary numbers below to illustrate the theory.)

Let's say your body typically wants 1000 calories at breakfast, and you eat 1000 calories with a heavy load of carbs. Carbohydrates with a high glycemic index cause your insulin to spike. That signals fat cells that they should start storing energy, and they do so, tucking away 300 of the 1000 calories you ate.

This means your body only gets to spend 700 of the 1000 calories you ate, and as such, it says "hey, I'm still hungry". You eat 300 calories worth of food. But your fat cells are still sucking up (X%) of what you eat into storage, due to the insulin reaction. So, your body gets 200 of those 300 it wants, and it stays a little bit hungry. (Or, more likely, your body wants 300, but you eat 500 to make it shut up.)

Carbs have the unfortunate habit of converting useful calories into fat storage prior to processing them for the purposes of nutrition. This means carb-heavy diets tend to cause unconscious overeating, and also constant feelings of hunger/cravings/etc.

One of the advantages of a paleo/keto diet is that they often avoid the type of carbohydrates that cause this problem, namely ones with a high glycemic index. This means when you eat 1000 calories, your fat cells don't skim any off the top before your metabolism gets to them, and you get the full 1000; this means you don't end up hungry after a meal, and don't suffer from the urge to snack/eat more. Because your body got all the energy it wanted, it doesn't start saying it's hungry again until it actually does need the nutrition, and you're more likely to eat closer to the correct amount for your body's needs.

The difference between the examples you give, 4500 of Paleo and 1200 of junk food, is primarily how they'd make your body react. 1200 of junk food would certainly be a caloric deficit, but you'd be ravenously hungry at that level. (I've done 1000 calories a day for 6 months straight - it's pretty awful for the first few months.) But with keto, you could eat 4500 calories in a day, but you won't want to. When I'm done eating a keto-style meal, I am completely uninterested in food until the next. Those meals, for me, are typically 1-2 small/medium brats with no bun. But if I go out and cheat, and grab a burger and fries, I've got to fight the urge to follow it up with some ice cream, even though the fries and burger combined are drastically more calories than the brats I was satisfied with the meal before.

It's really interesting stuff. The "calories-in, calories-out" model is completely right from a completely energy-based perspective, but it doesn't account for the side effects produced by the energy source, and how people react to them.

[tjogin]

This is pseudo science, there are droves of scientific literature that shows that meal timing is irrelevant and that as long as macronutrient content is similar, a calorie is a calorie.

[sgift]

And there are droves of scientific literature that show that meal timing is important and even if macronutrient content is similar, a calorie is not a calorie.

The simple fact is: No one was able to prove anything beyond shallow platitudes ("If you eat three tons of flesh each day you will get fat too!" "If you eat nothing for month you will get lean!").

[dalke]

A quick search of PubMed finds some recent (within the last year) papers like:

http://www.ncbi.nlm.nih.gov/pubmed/23357955 - "Timing of food intake predicts weight loss effectiveness" It starts "Background: There is emerging literature demonstrating a relationship between the timing of feeding and weight regulation in animals. However, whether the timing of food intake influences the success of a weight-loss diet in humans is unknown."

http://www.ncbi.nlm.nih.gov/pubmed/23167985 - "Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men."; "It is unclear how timing of exercise relative to meal ingestion influences substrate balance and metabolic responses."

These make me think that there isn't "droves of scientific literature" which show the importance of meal timing in humans, much less characterize the magnitude of the importance. (Eg, if there's a measurable 1% difference in overall effect on weight then it's statistically significant finding, but almost certainly not enough for most people to care about.)

[anthonyb]

Where is the parent saying anything about meal timing? It's about the effect on your body of a particular meal. Carbs and sugars spike insulin much more than fats or protein.

[tjogin]

That is an issue of meal timing. Individual meals doesn't matter. Transient insulin spikes are irrelevant, what matters is your overall expenditure vs intake.

[anthonyb]

Insulin spikes are completely relevant, since insulin signals your fat cells to take up energy from your blood stream. Now you have no energy and feel hungry again.

[tjogin]

It doesn't work that way. Show me a study that concludes that blood glucose levels have not been meaningfully increased after a meal due to it all going straight to adipose tissue -- in humans -- and I'll show you the next Nobel Prize winner.

Insulin spikes are irrelevant in so far as you will lose weight at a calorie deficit, insulin spikes or not. Also, fat can be synthesized in the absence of insulin spikes. http://www.jlr.org/content/30/11/1727

Physiologically, what matters is a caloric deficit. Execution wise, some foods make this easier than others, but that is highly individual.

"Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize" http://www.nejm.org/doi/full/10.1056/NEJMoa0804748

[anthonyb]

Yes it does work that way.

Steady levels of insulin make it much easier to maintain a caloric deficit. If your blood sugar is yo-yoing all over the place, you're going to get cravings, increase your risk of bingeing, etc.

While it's easy to fall back on 'calories in, calories out', weight loss has much more to do with psychology, physiology and compliance than physics.

edit: Here's a nice review article from Nature, which tells you all you need to know: http://141.213.232.243/bitstream/2027.42/62568/1/414799a.pdf

It starts:

  Despite periods of feeding and fasting, plasma
  glucose remains in a narrow range between 4
  and 7 mM in normal individuals.

[s_baby]

Don't feed the trolls.

[maxerickson]

There's a pretty good chance this is an over-analysis.

A daily 50 Calorie excess stacked up over 5 years amounts to a gain of about 25 pounds.

So it is certainly possible that a diet could be subtly tipping metabolism in the wrong direction, but between a complex explanation of more calories being stored as fat and a simple explanation of slightly too much consumption, I like the second one.

I guess that it is easy to consume large amounts of carbs makes them a frequent component of weight gain.