Which is the best diet for building a long-living, lean, fit body; low-carb, keto, low-fat, or high-protein?



If you're looking for the short answer, it's a high-protein diet.



Does that mean low-fat or low-carb diets never work? Not necessarily.



In this article, I'll explain a little of the pros and cons of each diet. By the end, you should be able to see why a high-protein diet is the way to go for almost everyone.



Before getting to the diets, though, I need to address some basic nutrition science, and tackle the topic of why "calories in, calories out" isn't as simple as your smartphone app would have you believe it to be.





Calories, Macronutrients, Basic Math



Obviously, the foods we eat contain calories. You see them posted on packages, restaurant menus, and alcohol bottles. When it’s not labeled, you can find it online.



We’ve grown to love the idea of counting calories because…well, we can count them. Not accurately, but we’ve been led to believe we can count them with a reasonable amount of accuracy.



We know that our love handles, saddle bags, and double chins are storage pouches of the calories we ate but didn’t need. And we believe that the way we get rid of them is to simply eat fewer calories.



To a certain extent, it does work.



When I was 15 years old, my ski jumping coach told me I needed to lose weight in order to be more competitive. I knew about calorie counts back then, so I decided to eat no more than 500 calories per day.



I filled up on diet pop and soda water, ate a few ounces of lunch meat each day and some vegetables, and once a week I went to the convenience store so I could splurge on salsa sandwiches.



Within a few months, I dropped my 5’10”, 154 lb frame down to 137 lbs.



I looked more like a meth addict than a ski jumper, but the scale said I did a good job with my diet.



Oh, in case you’re judging my parents, I lived in a dorm at Northern Michigan University, where they had an Olympic Training Center for ski jumping, for my junior year of high school. My parents were horrified the first time they saw me after my “successful” weight loss at a ski jumping tournament.



And herein lies one of the biggest problems about using only calories as a means of weight loss. 



You lose as much muscle as you lose body fat.



And at an extreme, you can cause significant damage to your metabolism, such as diet-induced hypothyroidism.



The Flaws In Calories In, Calories Out



At an extreme, like my 500 calorie diet, you can lose weight. It’s a dumb way to do it, but it’s possible.



More often, though, people are encouraged to follow a long-term, chronically restricted diet to “slowly” lose weight.



This is just as bad as my asinine anorexic method. But, probably more frustrating because you live in constant deprivation, but don’t see any results from your efforts.



We’ve been sold the idea that weight loss and weight gain is just about calories for decades now. It goes something like this:



A pound of fat contains 3500 calories. Therefore, to lose a pound per week of body fat, you just need to eat 500 calories per day fewer than you burn.



In business, this is called spreadsheet math. Spreadsheet math doesn’t account for any variables outside of the simple formula put into the spreadsheet. Just as businesses don’t grow according to numbers put into a spreadsheet, you don’t lose weight according to formulas either.



The calories in, calories out equation doesn’t account for the following:




Calorie counts on food labels and nutrition sites are not accurate.



People who estimate the amount of food they eat consistently underestimate their carbohydrate and fat-containing foods, and (from my experience) overestimate the amount of protein they eat.



Your resting metabolic rate varies dramatically based on lifestyle and nutrition choices.



The calorie expenditure on your favorite piece of cardio equipment, or on your heart rate monitor or movement track...