What Are Macros?
Macronutrients — protein, carbohydrate, and fat — are the three nutrients your body needs in large amounts, and the only ones that provide calories. Every food label you've ever read is just a different arrangement of these three.
Each macro carries a fixed energy value: protein and carbohydrate provide ~4 kcal per gram, while fat provides ~9 kcal per gram. That's the entire accounting system. A diet of 150g protein, 250g carbs, and 70g fat is (150 × 4) + (250 × 4) + (70 × 9) = 2,230 kcal — no matter which foods deliver those grams.
The hierarchy: calories first, macros second
Decades of metabolic ward studies and controlled feeding trials point to the same conclusion: total calorie balance determines whether you gain or lose weight. Macros sit one level below that — they shape what the change is made of:
- Protein — builds and preserves muscle, repairs tissue, and is by far the most satiating macro. It also has the highest thermic effect: roughly 20–30% of its calories are burned during digestion.2
- Carbohydrate — your body's preferred fuel for hard training. Stored as glycogen in muscle and liver, it powers high-intensity work and spares protein from being burned for energy.
- Fat — essential for hormone production, cell membranes, and absorbing vitamins A, D, E and K. "Essential" is literal: your body cannot make omega-3 and omega-6 fatty acids.
How to Set Your Macros
Each macro has a distinct job, which is why you set them in a specific order — not by copying someone's ratio:
The honest take: there is no magic ratio
You'll see "40/30/30" or "keto burns fat" claims everywhere. Controlled studies that equate calories and protein — including metabolic ward research comparing low-carb and low-fat diets — find no meaningful fat-loss advantage for any particular ratio. Once protein is adequate and fat clears the minimum, the carb-vs-fat split is context-dependent: hard training favours more carbs, sedentary preference may favour more fat, and adherence trumps everything.
Sample Splits by Goal
Examples below use an 80kg lifter. Your own numbers scale with body weight and total calories — which is exactly what our calculator does for you.
Flexible dieting vs "clean eating"
If calories and macros match, body composition outcomes are essentially the same whether the carbs come from rice or the occasional ice cream — that's what controlled comparisons show, and it's the basis of flexible dieting (IIFYM). But that's not a free pass for an 80%-junk diet:
- Satiety: whole foods — protein, fibre, volume — keep you fuller per calorie. Ultra-processed foods make it dramatically easier to overshoot; an NIH metabolic ward trial led by Kevin Hall found people spontaneously ate ~500 kcal/day more on an ultra-processed diet than a matched unprocessed one.3
- Micronutrients and fibre: macros say nothing about vitamins, minerals, or gut health. Mostly-whole-food diets cover these by default.
- Performance and recovery: training quality is consistently better when most carbs come from quality sources around sessions.
Put It Into Practice
Reading about macros changes nothing — your numbers do. These free tools turn the principles above into your personal targets in under a minute:
Frequently Asked Questions
Do I have to track macros to get results?
No. Macros are a tool, not a requirement. Calorie balance and adequate protein drive most results, and you can hit both with simpler habits — building meals around a protein source, watching portions. Tracking is most useful when progress stalls, when you're dieting to low body fat, or when you want to learn what's actually in your food. Many people track for a few months, internalise the lessons, then stop.
Are carbs bad for fat loss?
No. Controlled studies that match calories and protein consistently find similar fat loss on low-carb and low-fat diets. Low-carb diets often show faster initial scale drops — but that's mostly water and glycogen, not extra body fat. Carbs only cause fat gain when they push you into a surplus. If you train hard, carbs typically improve performance, which indirectly helps fat loss by letting you train with more volume and intensity.
What happens if I eat too little fat?
Chronically very low fat intake (well under ~0.5g/kg) can impair absorption of fat-soluble vitamins A, D, E and K, and is associated with reduced sex hormone levels in both men and women. Symptoms can include low energy, poor mood, dry skin, and disrupted menstrual cycles. Keeping fat at a minimum of roughly 0.6–1g/kg per day avoids these issues for most people.
Does the exact ratio matter if calories are equal?
Much less than most people think. Once protein is adequate and fat meets the hormonal minimum, shifting the remaining calories between carbs and fat has little measurable effect on body composition in controlled trials. The best split is the one that supports your training, controls your hunger, and fits foods you'll actually keep eating. Adherence beats optimisation.
Is alcohol a macro?
Effectively yes — alcohol provides ~7 kcal per gram, more energy-dense than protein or carbs and nearly as dense as fat. It provides no essential nutrients, temporarily suppresses fat oxidation while your body prioritises clearing it, and the calories in mixed drinks add up fast. You don't have to avoid it entirely, but count it within your calorie budget — usually by deducting it from your carb or fat allowance.
References
This guide is built from peer-reviewed research. Key sources:
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376–384. PubMed
- Westerterp KR. Diet induced thermogenesis. Nutrition & Metabolism. 2004;1:5. PubMed
- Hall KD, Ayuketah A, Brychta R, et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metabolism. 2019;30(1):67–77. PubMed