What Are Macros? Protein, Carbs and Fat Explained Simply

Protein is composed of amino acids — the building blocks the body uses to construct and repair muscle tissue, produce enzymes and hormones, support immune function, and maintain the structural integrity of skin, hair, and connective tissue. Of the 20 amino acids, nine are essential, meaning the body cannot synthesise them and they must be obtained from food. Complete protein sources — those containing all nine essential amino acids in adequate proportions — include animal products (meat, fish, eggs, dairy) and a few plant sources (soy, quinoa). Most plant proteins are incomplete but can be combined throughout the day to provide all essential amino acids.

Protein provides 4 calories per gram and has the highest thermic effect of any macronutrient: 20 to 30 percent of the calories in protein are used simply to digest and process it. This means that 100 calories of protein yields only 70 to 80 net calories after digestion — an inherent metabolic advantage for high-protein diets. Protein is also the most satiating macronutrient, reducing hunger hormones (ghrelin) and increasing satiety hormones (PYY, GLP-1) more effectively than carbohydrates or fat at the same calorie level.

For muscle maintenance, research consistently supports a minimum of 1.6 grams of protein per kilogram of body weight per day. For muscle building during a caloric surplus, 1.6 to 2.2 grams per kilogram is optimal. During fat loss in a caloric deficit — when the risk of muscle loss is highest — protein needs increase to the upper end of this range (2.0 to 2.4 grams per kilogram) to provide the amino acid substrate needed to counteract the catabolic signals of energy restriction.

Carbohydrates are the body's preferred fuel source for high-intensity activity and the exclusive fuel source for the brain under normal metabolic conditions (the brain can adapt to partial ketone use during carbohydrate restriction, but glucose remains its primary fuel). Carbohydrates provide 4 calories per gram and are classified as simple (monosaccharides and disaccharides like glucose, fructose, and sucrose) or complex (polysaccharides like starch and fibre).

The glycaemic index (GI) classifies carbohydrates by how rapidly they raise blood glucose. High-GI foods (white bread, sugar, white rice) cause rapid spikes and subsequent crashes in blood sugar, while low-GI foods (legumes, whole grains, most vegetables, and fruits) produce a slower, more sustained glucose response. However, the glycaemic load (GL) — which accounts for the portion size — is a more practical measure. Watermelon has a high GI but a low GL because a typical serving contains relatively little total carbohydrate.

Fibre is a form of carbohydrate that the human digestive system cannot break down. Soluble fibre (oats, legumes, fruits) dissolves in water and feeds beneficial gut bacteria, which produce short-chain fatty acids with anti-inflammatory properties. Insoluble fibre (vegetables, whole grains, nuts) adds bulk to stool and supports regular bowel movements. Current guidelines recommend 25 to 35 grams of fibre daily, but average intake in Western populations is roughly half that. Adequate fibre intake is consistently associated with reduced risk of cardiovascular disease, type 2 diabetes, and colorectal cancer in large population studies.

Carbohydrate needs are highly variable and depend primarily on activity level. Sedentary individuals may function well on 2 to 3 grams of carbohydrates per kilogram of body weight per day. Moderate exercisers benefit from 3 to 5 grams per kilogram. Endurance athletes or those performing high-volume training may need 6 to 10 grams per kilogram to maintain glycogen stores and performance.

Dietary fat provides 9 calories per gram — more than twice the energy density of protein or carbohydrates — which is why high-fat foods are so calorie-dense. But fat is far more than a concentrated energy source. It is essential for the absorption of fat-soluble vitamins (A, D, E, K), the production of hormones (including testosterone, oestrogen, and cortisol), the integrity of cell membranes, brain function (the brain is roughly 60 percent fat by dry weight), and the insulation and protection of organs.

Fats are classified by their chemical structure. Saturated fats (found in red meat, butter, coconut oil, and full-fat dairy) are solid at room temperature and have been traditionally linked to cardiovascular risk, though recent research has nuanced this view considerably — the health impact depends on the specific saturated fatty acids and what they replace in the diet. Monounsaturated fats (olive oil, avocados, nuts) are consistently associated with cardiovascular benefit. Polyunsaturated fats include omega-6 (seed oils, nuts) and omega-3 (fatty fish, flaxseed, walnuts) fatty acids. Omega-3s are anti-inflammatory and most Western diets are deficient in them relative to omega-6 intake.

Trans fats — artificially produced through partial hydrogenation of vegetable oils — are unambiguously harmful and have been banned or restricted in most countries. Minimum fat intake for hormonal health is approximately 0.5 to 0.6 grams per kilogram of body weight per day. Going below this level, particularly for extended periods, can suppress testosterone and oestrogen production, impair vitamin absorption, and negatively affect mood and cognitive function. Most evidence-based guidelines recommend fat intake of 0.7 to 1.2 grams per kilogram per day for the general population.

Setting macros follows a hierarchy: total calories first, then protein, then fat, then carbohydrates fill the remainder. This order reflects the relative importance and rigidity of each variable. Step one: determine your TDEE and decide on your caloric target (deficit for fat loss, surplus for muscle gain, maintenance for body recomposition). Step two: set protein at 1.6 to 2.2 grams per kilogram of body weight (use the higher end during fat loss). Step three: set fat at 0.7 to 1.2 grams per kilogram. Step four: allocate remaining calories to carbohydrates.

Worked example for a 75-kilogram person targeting fat loss at 2,000 calories per day: Protein at 2.0 grams per kilogram equals 150 grams (600 calories). Fat at 0.9 grams per kilogram equals 67.5 grams (608 calories). Remaining calories for carbohydrates: 2,000 minus 600 minus 608 equals 792 calories, which is 198 grams of carbohydrates. The resulting macro split is approximately 30 percent protein, 30 percent fat, 40 percent carbohydrates.

This is a balanced approach that works well for most people. However, individual preferences and responses matter. Some people feel better and adhere more easily to higher-carb, lower-fat diets. Others prefer higher-fat, lower-carb approaches. As long as protein is adequate and total calories are correct, the specific carb-to-fat ratio has a relatively small impact on body composition outcomes. The best macro split is the one you can sustain consistently — compliance trumps optimisation in every dietary context.

Macro tracking typically involves using a food logging app (MyFitnessPal, Cronometer, MacroFactor, and others) to record everything you eat and monitor your daily protein, carbohydrate, and fat totals against your targets. A digital kitchen scale is essential for accuracy — measuring food by weight (in grams) is significantly more precise than measuring by volume or estimating visually. Most people who fail at macro tracking do so because they estimate portions rather than weighing them.

Practical tracking tips: log your food in advance when possible (plan your meals in the morning and pre-log them, then adjust as the day progresses). Focus on hitting your protein target first — if other macros are slightly off, it matters less. Give yourself a daily range rather than an exact number: plus or minus 10 grams for protein and plus or minus 5 to 10 grams for fat and carbohydrates. Perfect daily adherence is unnecessary; weekly averages matter far more than any single day.

Macro tracking is a powerful educational tool, but it is not meant to be a permanent practice for most people. After three to six months of consistent tracking, most people develop an intuitive understanding of portion sizes and the macronutrient composition of common foods. At that point, you can transition to a more relaxed approach — tracking periodically (one week per month, for example) to recalibrate your intuition, while eating intuitively the rest of the time. For people with a history of disordered eating, macro tracking may trigger obsessive behaviours. If tracking causes anxiety, guilt, or a preoccupation with numbers that detracts from your quality of life, stop tracking and work with a registered dietitian to develop a healthier approach.