Protein, carbs and fats: macronutrient guide for beginners

What macronutrients are and why you should know them

Macronutrients are the three families of molecules that make up everything you eat: protein, carbohydrate and fat. They are called "macro" because you need them in large quantities (grams), unlike micronutrients — vitamins and minerals — which are measured in milligrams. Each macronutrient has a specific job in your body, and the balance between them, what dietitians call your macro ratio, has a direct impact on your energy, your body composition, your athletic performance and your mood.

Understanding macros is not just for bodybuilders or athletes. A study published in the New England Journal of Medicine in 2009 — the POUNDS LOST trial — showed that what really determines weight loss is total calories, not the macro split. But the macro split does affect how much muscle you keep, how hungry you feel and how much energy you have along the way. Put another way: calories determine what you weigh, macros determine how you look and how you feel.

Protein: the macronutrient that builds and repairs

Proteins are made of amino acids, the bricks your body uses to build and repair tissue. There are 20 amino acids in total, nine of which are "essential": your body cannot manufacture them, so they have to come from food. When you eat protein, your digestive system breaks it down into individual amino acids, which are then used to repair muscle fibres damaged by exercise, manufacture enzymes and hormones, maintain skin, hair and nails, and support your immune system.

How much protein you need for your goal

The official recommended daily allowance is 0.8 g per kg of bodyweight, but that figure was designed to prevent deficiency, not to optimise health or body composition. Modern research points to substantially higher amounts:

• Sedentary with no physique goal: 1.0-1.2 g/kg (example: 70 kg = 70-84 g/day)
• Active and losing fat: 1.6-2.0 g/kg (example: 70 kg = 112-140 g/day). High protein during a deficit protects your muscle and keeps you full
• Building muscle: 1.8-2.2 g/kg (example: 70 kg = 126-154 g/day). New muscle needs amino acids as raw material
• Competitive athlete: 2.0-2.5 g/kg. More training means more repair, which means more protein
• Over 60: 1.2-1.6 g/kg. The efficiency of protein synthesis declines with age — the phenomenon known as anabolic resistance

The best protein sources, with real numbers

Not all protein sources are equal. Quality is measured by amino acid profile and digestibility (biological value). These have the best protein-to-calorie ratios:

• Chicken breast, skinless: 31 g protein, 165 kcal per 100 g — biological value 79
• Egg whites: 11 g protein, 52 kcal per 100 g — biological value 100, the reference standard
• Salmon: 25 g protein, 208 kcal per 100 g — plus EPA and DHA omega-3
• Plain Greek yogurt: 10 g protein, 59 kcal per 100 g — with probiotics for gut health
• Lentils: 9 g protein, 116 kcal per 100 g cooked — combined with grains they form a complete protein
• Firm tofu: 8 g protein, 76 kcal per 100 g — the best plant option, with all essential amino acids
• Tinned tuna in water: 26 g protein, 116 kcal per 100 g — cheap and practical, though worth moderating because of mercury

Carbohydrate: the energy source your brain needs

Carbohydrate is the preferred fuel of your brain, your nervous system and your muscles during high-intensity exercise. Your brain consumes roughly 120 g of glucose a day, about 480 kcal, which is 20% of your total energy expenditure despite the brain being only 2% of your bodyweight. When you cut carbohydrate drastically, as in a ketogenic diet, your body enters ketosis and uses ketones as an alternative fuel — but there is an adaptation period of two to four weeks during which cognitive and physical performance drop noticeably.

Simple versus complex carbs: the real difference

The key distinction is not "good versus bad" but speed of absorption. Simple carbohydrates (table sugar, juice, sweets, white bread) are absorbed quickly, raise blood glucose sharply, trigger an insulin spike and leave you hungry an hour or two later. Complex carbohydrates (oats, brown rice, sweet potato, legumes, vegetables) are absorbed slowly thanks to their fibre content, deliver steady energy for hours and keep you satisfied. The glycemic index (GI) measures that absorption speed on a scale from 0 to 100.

• High GI (over 70): white bread (75), white rice (73), boiled potato (78), watermelon (76)
• Medium GI (56-69): brown rice (68), ripe banana (62), honey (61)
• Low GI (under 55): oats (55), lentils (32), apple (36), yogurt (41), sweet potato (44)

Fat: the most misunderstood macronutrient

Fat was demonised for decades by the food industry, which replaced it with sugar, and by government guidelines built on incomplete science. We now know fat is essential for hormone production (testosterone, oestrogen, cortisol), for absorbing the fat-soluble vitamins A, D, E and K, for brain health — your brain is roughly 60% fat — and for protecting internal organs. Cutting fat out of your diet is not just unnecessary, it is harmful.

• Monounsaturated fats (the best): extra virgin olive oil, avocado, almonds, olives. They lower LDL cholesterol and protect the heart
• Polyunsaturated fats (essential): salmon, sardines, walnuts, flaxseed. These include omega-3 (anti-inflammatory) and omega-6. The ideal omega-6 to omega-3 ratio is around 3:1; the modern Western diet runs closer to 15:1
• Saturated fats (in moderation): eggs, red meat, butter, coconut. Recent research suggests their cardiovascular impact is smaller than once believed, but keeping them under 10% of total calories remains sensible
• Trans fats (always avoid): margarine, industrial pastry, ultra-processed food. These are the only genuinely harmful fats. Since 2018 the FDA has progressively banned them in the United States

How to split your macros for your goal

There is no universally perfect split, but these are the recommendations supported by current literature:

• Losing fat while keeping muscle: 30% protein, 35% carbohydrate, 35% fat. On a 2,000 kcal TDEE that is 150 g protein, 175 g carbohydrate, 78 g fat
• Building muscle (bulking): 25% protein, 50% carbohydrate, 25% fat. Higher carbohydrate provides energy for hard training and supports protein synthesis via insulin
• General health and maintenance: 25% protein, 45% carbohydrate, 30% fat. The most flexible and sustainable split over the long term
• Ketogenic: 25% protein, 5% carbohydrate, 70% fat. Effective for epilepsy and some cases of insulin resistance, but hard to sustain and not superior to other diets for weight loss according to the evidence

How to track macros without losing your mind

The biggest mistake with macro tracking is trying to be perfect from day one. Start with protein alone — it is the most important macro and the hardest to hit. Once you reach your protein target consistently, which usually takes two to three weeks, add total calories. Carbohydrate and fat will settle themselves if protein and calories are under control. With an app like Renzy that scans your meal from a photo, tracking comes down to taking your phone out and pressing the button. The AI returns every macro instantly, with nothing to search, weigh or calculate.