I ponder macro-nutrition needs a whole bunch. Here’s what I have handy, though my technical references are scattered and omitted.
There’s always a need for roughage, vitamins, and minerals, which come from foods with very low calories/kilojoules. Aside from that, the three main macros have specific needs.
A body needs 125 grams of carbs for your brain/nerves; just under 1 gram of protein per kilo of lean body mass to maintain tissues/muscles; and around 30g of fat for cellular and neurological structures. This is usually around 1200 kcal per day, but varies by person 10-20 percent.
Anything else you eat is either poop, or gets converted to sugar. Sugar is burned if it’s needed immediately for exercise (growing, standing, walking, cardio, whatever, anything other than sleeping). Any sugar that is not immediately needed is stored in muscles as glycogen, up to around 4% of your muscle mass. All sugar past that is turned into fat and stored in our fat cells.
This is where “whole grains” comes into play. If it’s not ground up, it takes longer to break it down. However, if you take grains, and mill them into a powder, IT IS NOT WHOLE GRAINS. Just because there is fiber in the food does not mean it’s slow to absorb. The less processed the food, the longer time period over which it trickles energy into your body. If it’s super processed, it all absorbs very quickly, and your body may have trouble figuring out what to do with it unless you’re depleted already.
This is also where some insulin resistance comes from, and why diabetics have normal sugar metabolism in their muscles during exercise, even if they are short on insulin, or are resistant to it. Resistance is GLUT4 which causes glucose receptors to move to the cell membrane, but exercise does the same thing – muscle is hungry, it asks for more. Muscle is not hungry, it asks for less, even if you try to overfeed it. Where would it put this excess sugar? It can only store so much.
During exercise, your fat cells can liberate about 90% of your weight in pounds as usable calories per hour. For me, it’s about 260 calories. The gap is made up from glycogen in the muscles, which is good for just about 90 minutes. If you exercise hard, and stop at 60, and rest for 30, those 30 mins still use up that glycogen for delayed processes, cleanup, etc.
Eating carbs cannot provide as much energy as glycogen, but it’s the next best thing. Also, if you’re fasting, your glycogen reserves get burned up pretty quickly. Glycogen is 3:1 water to sugar, so this is why the first week of dieting is so awesome. No, that’s not fat. It’s muscle energy.
Any energy deficiency not covered by food will be covered by muscle damage. About the same number of calories can be broken down out of injured muscle cells. For me, this is a total of muscle and fat sourced calories of about 520 calories per hour. If I exercise for 3 hours with no food, then my power output drops to 130 watts, which is about 520 calories per hour.
The best option to limit muscle damage, limit recovery time, and optimize exercise benefits when going for more than your glycoge, is to eat as much every hour as you burn, minus the calories that can come from fat. Staying carb focussed can give more energy, and can be easier to absorb, though for some people, this slows the breakdown of body fat.
Staying fat focussed keeps the fat burn mechanisms running, but it takes twice as much oxygen, which means you’re hear-rate limited. It’s less about muscle conditioning then, and more about cardiovascular improvement.
Staying protein focussed is tougher on the kidneys. The aminos have to be converted for use as fuel, and that’s a lot of extra ammonia to pee out. That can be an issue when dehydration might already be at play.