How does nutrition work?

(I don’t know whether to be embarrassed by the naivety of this question or if I’m on the cutting edge of nutrition science with it.)

What if, um, hypothetically, you ate a lot of candy but also did intermittent fasting and exercise and stayed in your ideal weight range?

Like how would you rank the following 4 people:

Rita Thogsnogger eats Real food and is Thin.
Russ Flingstinger eats Real food and is Fat.
Jan Thistletwister eats Junk food but is Thin.
Jess Fozzlebottom eats Junk food and is Fat.

Obviously Rita T is healthiest and Jess F is unhealthiest. But how do you rank Russ F and Jan T? And are they closer to Rita T or to Jess F?

If the unhealthiness of sugar is mostly that it causes you to carry excess fat then Jan T isn’t too far behind Rita T, and maybe it’s worth it for Jan if they like junk food enough.

(And obviously there’s a whole continuum between “thin” and “fat” and between “real” and “junk”. I’d just love to have a better sense of how unhealthy it is to take a step in the “junk” direction without also taking a step in the “fat” direction.)

Long-term, or short-term?

Eating your calories as primarily sugar long term is going to have some effects that take a while to show up, things like insulin resistance and diabetes.

Depending upon how much sugar we’re talking, I’d expect issues from lack of fiber, ranging from poop and butt issues to increased chances of colon cancer.

There’s been talk for a long time about being “fat but fit”. I am not a professional in this, but it is unclear to me if it is certainly real, certainly not real, or limited to certain cohorts.

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How did I forget the exciting world of nutrional deficiencies? Beriberi, scurvy, pellagra…

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Great points! Let’s further assume that this hypothetical person beeminds a reasonable minimum of fiber and vegetables, maybe vitamins?

But long-term, not short-term. And I’m not saying primarily sugar calories, and maybe there’s a threshold where it becomes really unhealthy, but that’s the problem: I don’t feel like I have a sense of how to make the tradeoffs! Or even how to conceptualize it. Like could I imagine that my body has a finite lifetime supply of insulin (or just so much wear and tear that my pancreas can handle) and then I’ll have diabetes? Or some kind of reason like that for why every additional spoonful of sugar has long-term consequences that outweigh the short-term yumminess, even with bodyweight, fiber, vitamins, etc held constant?

Even if you’re beeminding getting your fiber, veggies, vitamins… there’s minerals, protein/essential amino acids, healthy fats, and phytonutrients. Any amount of sugary foods you consume are taking up space where healthier things could fit. The finite insulin/pancreas wearing out examples don’t really make sense because sugar consumed along with a wholesome meal that includes fiber, protein, fat… or as part of a fibrous, high water content piece of fruit affects you differently than literally eating a spoonful of sugar. And if you’re exercising vigorously while eating the spoonful of sugar, it would go straight to energy for muscles and not be excess/therefor stored as fat. Fat accumulation is what increases our chances of diabetes because fat tissue is a hormone disrupter. Fat accumulation happens when we overeat. It just so happens that we tend to overeat highly sweet, extra palatable processed foods more than whole real foods, and there’s usually sugar in them.


I’d suggest to unmarry fitness and nutrition for now.

In nutrition, you can basically do a hierarchy as so often. High to low impact:
Net Caloric Intake < Macronutrient Composition < Micronutrient Composition < Intake Timing

You can lose weight on a twinkie diet and you can gain on an IF raw vegan diet. However, that will usually bring you to some kind of nutrient deficiency. (Workouts impact net caloric intake but you can’t outrun a bad diet. A marathon should burn around 2000 calories, so 2 big macs fries and a 2L coke will easily offset that.)

Usually it’s a good idea to move away from “good food bad food” and more towards IIFYM (If it fits your macros). Is a burger bad? Maybe it has too many carbs, but maybe it fits today’s macros and actually would not impact you negatively.

People recommend cooking yourself, because that usually means you’ll have less processed foods and a better control of carbs and fats. Processed foods tend to contain more carbs and fats, because these tend to make food yummy (Chocolate anyone?). Another way to think about it is calorie density. Brokkoli? Huge volume, few calories. Cheese? Dense block of fat. (100g cheddar : 400kcal : 1150g Brokkoli)

Ranging on the caloric intake Jan T is obviously doing better than Russ F. Russ F may be doing better on the Macro and Micro nutrients, however, with a standard diet, you will most likely not become nutrient deficient, turns out you could survive on potatoes pretty much. The health impact of abdominal fat, unfortunately, is pretty high (cardiovascular, inflamation scores, longevity). Ironically, that is often a problem, not every fat person digs into the golden M for 3 meals a day. They eat a nice salad, but spice it up with salmon and mozzarella, which, depending on the amount, can bring a salad to over 1000kcal easily. (With 2k kcal being the “average adult male” intake.) If you then “treat yourself because you had just a salad for dinner”, weight easily increases.

Just a ‘quick’ note on fitness (cardiovascular etc) of thin and fat people. It’s basically impossible to see if a person works out or not. Granted, an overweight person should probably not run said marathon due too the impact on joints (mostly knees, bit feet and hip), but you don’t know if they regularly do Crossfit, lift a ton or are a couchpotato. On thin people it’s often a bit easier to see if they’re training weights, due to fat not “masking” the sweet sweet biceps. But do they run? Aerial acrobatics? Climbing? So many climbers look like they are just thin, then scale a window pane without breaking a sweat.