Macros are the three nutrients that supply your calories: protein, fat and carbohydrate. "Splitting your macros" means deciding how many grams of each to eat. There is a simple order that suits most people, and it matches what the research can and cannot back up.
The short version
- Set protein first, in grams per kilogram of body weight. 1.6 is a good standard, and 2.0 to 2.4 are reasonable while eating less.
- Set fat next, as 20 to 35% of calories. Carbs take everything that is left.
- Inside those ranges the evidence for one best split is thin, so pick what you can stick to.
Step 1: start from calories
Everything divides your daily calories. Protein and carbs give 4 calories a gram and fat gives 9, the general factors used on US food labels. If you do not have a calorie number, the calorie calculator estimates one.
Step 2: protein
- 0.8 g per kg is the Recommended Dietary Allowance, a floor for avoiding deficiency.
- 1.4 to 2.0 g per kg is what the International Society of Sports Nutrition position stand gives for people who exercise (Jager and colleagues, 2017).
- About 1.6 g per kg is where muscle gains from lifting leveled off, on average, across 49 trials. The uncertainty around that figure ran from about 1.0 to 2.2 (Morton and colleagues, 2018).
- 2.3 to 3.1 g per kg is the position stand's range for lean, resistance-trained people eating below maintenance. It is for people who already lift and are already lean.
Step 3: fat
The Dietary Guidelines for Americans give adults a range of 20 to 35% of calories from fat. Writers for lifters give 15 to 30% while dieting (Helms and colleagues, 2014) and 0.5 to 1.5 grams per kilogram (Iraki and colleagues, 2019). A middle choice like 25% sits inside all of them.
Step 4: carbs fill the rest
Carbs are what remains after protein and fat, divided by 4. The Dietary Guidelines range is 45 to 65% of calories, with an RDA of 130 grams a day. For people who lift hard, a review of bodybuilders' off-season diets suggests at least 3 to 5 grams per kilogram. Fiber has its own goal of 14 grams per 1,000 calories.
A worked example
A 70 kg person eating 2,000 calories, at 1.6 g per kg of protein and 25% fat:
- Protein: 70 x 1.6 = 112 g, which is 448 calories.
- Fat: 2,000 x 0.25 = 500 calories, divided by 9 = 56 g (504 calories).
- Carbs: (2,000 - 448 - 504) / 4 = 262 g.
- As shares of calories: protein 22%, fat 25%, carbs 52%. Fiber goal: 2 x 14 = 28 g.
Eating less leaves less for carbs, since protein is fixed by weight. At 1,600 calories the same person gets 112 g protein, 44 g fat and 189 g carbs, a drop of 73 g of carbs.
When you are eating less
Protein stays tied to your weight, so a lower calorie total comes out of fat and carbs. That is why leaner lifters in a deficit are given higher protein numbers: the research on losing weight while keeping muscle points toward more protein, not less. You can try your own numbers in the macro split calculator, which flags a split that runs out of calories, falls under the fat or carb ranges, or pushes protein above 35% of calories.
Vital works the same way. Protein presets are Standard (about 1.6 g per kg), High (about 2.0) and Very high (about 2.4), fat defaults to 25% of calories, and carbs take what is left. Every target can be edited by hand.
What we are less sure about
- No one best split. The ranges overlap because the evidence does not pick a winner. The ranges are decades old, and the National Academies published a 2024 letter report asking whether macronutrient ranges are still the right tool.
- Who the protein studies cover. Most come from lifters and athletes. The 1.6 figure is an average with a wide band around it, not a cliff.
- The carb number. The "3 to 5 g per kg" figure comes from a narrative review of bodybuilders' diets, not from trials, so it is a sensible guide for hard training and not a requirement.
- Meal timing. One review suggests about 0.4 to 0.55 g of protein per kg per meal, but it also found timing and meal frequency had little effect on fat loss or lean mass retention during dieting. Total daily intake is the safer thing to watch.
Sources
- U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025, Appendix 7: Nutritional goals for age-sex groups. PDF
- Jager R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20. doi:10.1186/s12970-017-0177-8
- 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. Br J Sports Med 2018;52(6):376-384. doi:10.1136/bjsports-2017-097608
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr 2014;11:20. doi:10.1186/1550-2783-11-20
- Iraki J, Fitschen P, Espinar S, Helms E. Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports (Basel) 2019;7(7):154. doi:10.3390/sports7070154
- Code of Federal Regulations, Title 21, section 101.9: Nutrition labeling of food (Cornell Legal Information Institute copy). 21 CFR 101.9
- National Academies of Sciences, Engineering, and Medicine. Rethinking the Acceptable Macronutrient Distribution Range for the 21st Century: A Letter Report. 2024. doi:10.17226/27957
Written November 5, 2026. This is general information, not medical advice. Talk to a doctor or dietitian before big changes to how you eat or train, especially with a medical condition or a history of disordered eating.