This is currently a huge work in progress, but the goal is to create three sections: (1) the calories-in-calories-out model (2) other lessons from the literature, and (3) a model that attempts to unify that literature.
Weight Set Point
Set point theory is, rather vaguely, the notion that the body tends towards a set weight, and that deviations from this weight (e.g. via diet or exercise) are fighting an uphill battle.
Under the boring interpretation, this theory is basically just a restatement of the fact that it takes more calories to maintain more weight and fewer calories to maintain less weight, which tends to make weight stable. We know this is true: see the BMR formulas and note that non-BMR calories almost always (roughly) scale with weight (e.g. exercise, NEAT, etc). This is presumably why if you start eating 10 calories per day more forever, you won't gain infinite weight.
A somewhat more interesting interpretation is that when your net-energy is high, you fidget more, while when it is low/negative, you fidget less - thereby further tending to make weight stable. This is also true (see NEAT, above).
Another interpretation is that the bodies' response is more powerful at preventing you from losing weight - that is, if I eat a lot, I'll fidget a lot more; if I eat a little, I'll only figet a little less. I've never seen any evidence in favor of this, but I have seen evidence against Leibel Bray.
Finally, there's a notion that if you've been obese for a while, and then lose weight, your BMR/NEAT will be permanently lower (possibly due to permanently increased body fat) compared to someone of the same weight but who was never obese. Again, I've never seen any evidence in favor of this, but I have seen evidence agains:
Leibel had 24 subjects gain 10% more weight and then lose it again. They found no change in total energy expenditure or body fat afterwards.
Salans had five subjects gain ~20% more weight and then lose it again. They found no changes in body fat percentage afterwards.
In Bray, the author gained 13% more weight over 10 weeks and then lost it again in 6, which he "maintained with no trouble ever since". Four volunteers did likewise.
So, the tl;dr on set-point is that as far as I can tell losing and gaining weight are equally "difficult" in the sense that eating 100 kcal more or 100 kcal less will have the same effect on weight (but in opposite directions). It looks like once you lose weight, it appears that its as if you never put it on in the first place.
Instead, the only reasonable interpretation of a weight "set point" is more abstract: left to their own devices, people's weights will generally return to a specific point. Some of this is just metabolic: since energy expenditure tends to be positively affected by both energy surplus and weight, changes in weight are muted. However, given the wide array of weights actually held by real people, it seems likely there is more to this story.
This is generally the perspective on weight offered as an alternative to CICO: how can someone reduce their "set point"? I feel I should explicitly point out: I don't see these perspectives as contradictory - instead I see them as complimentary (like the duality principle in optimization Duality (optimization)).
Whereas CICO explains the rise in obesity as people eating more, the set point perspective asks why people feel the need to eat more. Explanations I've seen given include
Modern food today is super tasty and this psychologically affects some people more than others Book Review: The Hungry Brain Hashim (see https://slimemoldtimemold.com/2021/07/23/a-chemical-hunger-interlude-b-the-nutrient-sludge-diet/ for a rebuttal)
Chemical contaminants are causing our bodies to malfunction and different people have different levels of these contaminants https://slimemoldtimemold.com/2021/07/07/a-chemical-hunger-part-i-mysteries/.
We'll come back to this dual perspective later.
A meta-analysis established a correlation between lack of sleep and weight gain Patel. A causal relationship was later established, finding that sleeping 5 hours rather than 9 caused a ~5% increase in energy expenditure and a ~6% increase in calorie intake (almost all after dinner). Over 5 days the net effect on energy balance was ~55 kcal/d, but it wasn't statistically significant Markwald. In my opinion, this study loaded the conclusions in favor of finding weight gain: its participants were kept in a single room with snacks and pre-made meals were 1500 kcal each.
This general finding has been confirmed by a meta-analysis Capers: sleep restriction increases energy consumption and energy expenditure with inconsistent effects on energy balance/weight change.
So sleep has minimal effect on weight? Not necessarily. First, Scott Siskind thinks sleep matters The Physics Diet?. Second, the people in the above study weren't trying to accomplish any weight-related goals. A study of people actually trying to lose weight found that pairing it with an intervention to improve sleep led to over double the weight loss over 12 weeks (equivalent to 250 kcal/d more) (p~0.04) Logue.
These findings actually make intuitive sense to me: sleep improves our ability to achieve our goals but doesn't just magically make us less hungry.
A meta-analysis finds that 81% of the variance in BMI is genetic for European/American men in the modern day and roughly 12% is due to shared environment Elks. The genetic contribution is 2% higher for women and has has grown by 7% over the last 24 years. Finally, it changes with age too:
[ Inspired by https://slimemoldtimemold.com/2021/07/07/a-chemical-hunger-part-i-mysteries/ ]
People at higher elevations are less likely to be obese Association of elevation, urbanization and ambient temperature with obesity prevalence in the United States, even after controlling for demographic factors evangambit, and even persisting after also controlling for physical activity, access to healthy foods, smoking, and a "food environment index" Explaining the inverse association between altitude and obesity. However, after all the controls the association is weakened: a 1000m change in elevation was associated with a 1.8pp decrease in obesity prevalence.
In this case, we can also even a causal effect based on a quasi-experiment in the US military Lower obesity rate during residence at high altitude among a military population with frequent migration: a quasi experimental model for investigating spatial causation. Over 7 years, those stationed below 0.98 km had a ~26% chance of becoming obese while those stationed above 1.96 km had a 15% chance. That's a 10pp change for an average elevation change of ~1800 meters, about 3 times smaller than the association founder above.
Studies of Everest climbers find that they generally eat far less at higher elevations Human responses to extreme altitudes.
Some highlights from Leaf:
One study fed participants muffins made with either sunflower oil or palm oil. Both groups saw similar increases in body weight, but the former gained much less fat mass. One interpretation is that saturated fat causes more fat gain than polyunsaturated fat.
One study fed subjects 20%, 40%, and 60% energy surpluses. The percent of gained weight that was fat was equal in all three groups. The higher-surplus groups gained more water weight.
High-protein diets cause smaller weight gain (given equal caloric intake) and cause less of the gained weight to be fat. Protein is particularly beneficial in gaining muscle mass while performing resistance training (see also here.
TODO Stenman The relationship between gut microbiota and weight gain in humans Gut microbiota modifications and weight gain in early life
Glycemic Index, etc
Several studies have been interpreted in popular culture as showing that its easier for men to lose weight than women. Is this true? The answer is that the question is underspecified. For instance, the pop-culture articles are typically based on studies that find that if you give the same number of calories to men and women find men lose more weight Christensen. However, is it easier? That's really a psychological question. Given their different typical sizes and the fact that hunger is a hard-to-measure psychological phenomenon, the answer is unclear.
A more interesting question is whether a difference exists between the sexes' weight gains given the same caloric surplus (TODO).
Misc literature reviews
Madigan Ohsiek Poynter Shaw Obert Burke Leaf
The Exercise Literature
This is all nice and dandy for lab results, but what about in real life? A 1980 meta-analysis of previously-sedentary participants on unplanned diets found an average effect size of 0.24 lbs/wk (SE=0.003 lb/wk) Epstein.
A 2011 meta-analysis of participants on unplanned diets found 6-month programs reduced weight by 3.5 lb (95% CI=3.4 to 3.6 lb) while 12 month programs reduced weight by 3.7 lb (95% CI=2.4 lb to 5.0 lb). They found waist reductions of ~0.8", which suggests little muscle mass was gained. The review only included studies with at least 2 hours of exercise per week Thorogood. Now, if we use very pessimistic assumptions (no increase in NEET (see below), 300 kcal burned per week), we should predict a two pound loss after 6 months, so its not actually obvious from this that NEET and/or more eating is actually making exercise less potent. Still, losing 4 pounds after a year of effort is nothing to write home about.
What about dosage? Aerobic exercise alone results in clinically significant weight loss for men and women: midwest exercise trial 2 assigned people to exercise 5 d/wk for 10 months, burning either 2000 kcal or 3000 kcal per week. The former group lost 10 lb (SE~3 lb) while the latter lost 13 lb (SE~4 lb). This is unable to reject either no difference from extra exercise or proportional difference.
Figure 6 from this literature review suggests increasing energy expenditure from 1000 to 2500 kcal results in only ~40% more weight loss, suggesting diminishing returns - however, there are no standard errors given The role of exercise for weight loss and maintenance:
Finally, Catenacci concludes that all the above is just because of insufficient exercise, finding that in "prospective studies that prescribed high levels of exercise, enrolled individuals achieved substantially greater weight loss—comparable to that obtained after similar energy deficits were produced by caloric restriction...The addition of physical activity (60–90 min) to a dietary intervention substantially increases the odds of successful long-term weight-loss maintenance and might be essential for most overweight and obese individuals to maintain weight loss."
TODO Bellicha Egberts Curioni
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