Fats Explained — Saturated, Unsaturated and How Much You Need
Fat is the most energy-dense macronutrient at 9 kcal per gram — more than double carbohydrate or protein — and that single fact explains both its reputation and its usefulness. It carries the fat-soluble vitamins (A, D, E and K), supplies the essential fatty acids the body cannot make, and is the raw material for hormones including testosterone. A diet too low in fat does not just feel joyless; it can leave hormone production and vitamin absorption short.
The headline answer is that most adults do well on 20–35% of calories from fat, with saturated fat kept below 10% of calories (World Health Organization and most national guidelines). At 2,000 kcal a day that is roughly 44–78 g of total fat, of which no more than about 22 g should be saturated. The type of fat matters far more than the total: swapping saturated fat for unsaturated fat improves blood cholesterol, while simply adding fat on top of an already adequate diet adds calories.
Use the calculator
Start with your own numbers: try our macro calculator to work out your figures before applying anything on this page. The worked examples below use round numbers so you can follow the maths; the calculators use your real weight, height, age and goal.
Related reading: Carbs Explained, Keto Diet Explained, What Are Macros?. You can also browse the full guides section for the rest of the series.
The key points
Saturated fat raises LDL cholesterol. Saturated fats — butter, fatty meat, cheese, coconut oil, palm oil — raise LDL ('bad') cholesterol more than any other dietary factor, and the evidence linking high saturated-fat intake to heart disease is among the strongest in nutrition (WHO, 2023). That does not make a single food 'toxic'; it makes the pattern matter. A diet built on butter, cheese and fatty meat every day is a different proposition from one that uses them occasionally.
Unsaturated fats are the ones to favour. Monounsaturated fats (olive oil, rapeseed oil, avocados, nuts) and polyunsaturated fats (oily fish, walnuts, flaxseed, sunflower oil) lower LDL cholesterol when they replace saturated fat, and oily fish supply the long-chain omega-3s EPA and DHA, which the body makes poorly from plant sources. The practical rule is simple: cook with olive or rapeseed oil, eat oily fish once or twice a week, and snack on nuts instead of biscuits.
Fat is essential, but it is easy to overeat. Because fat carries 9 kcal per gram, small amounts add up fast: a tablespoon of oil is about 120 kcal, a handful of nuts about 180 kcal, and a restaurant portion of chips can carry 40 g of fat before you notice. That density is why fat is the easiest macronutrient to overshoot in a fat-loss diet — and why measuring oil and butter for two weeks is often more useful than any new diet rule.
Very-low-fat diets have their own problems. Dropping fat below about 15% of calories makes food bland, reduces absorption of fat-soluble vitamins, and can lower testosterone in men on a calorie deficit. The sweet spot for most people is 25–35% of calories: enough to make food satisfying and hormones supported, low enough to leave room for the protein and carbohydrate that drive training and fullness.
At a glance
| Food | Total fat per 100 g | Saturated fat | Main type |
|---|---|---|---|
| Olive oil | 100 g | 14 g | Monounsaturated |
| Butter | 81 g | 51 g | Saturated |
| Almonds | 49 g | 3.7 g | Monounsaturated |
| Salmon (raw) | 13 g | 3 g | Omega-3 polyunsaturated |
| Avocado | 15 g | 2 g | Monounsaturated |
| Cheddar cheese | 33 g | 21 g | Saturated |
| Chicken breast (raw) | 3.6 g | 1 g | Low fat overall |
| Mayonnaise | 75 g | 11 g | Mostly unsaturated |
Figures are typical USDA FoodData Central values. Note how quickly fat adds up: 100 g of almonds carries nearly 600 kcal, and a single tablespoon of oil (about 14 g) carries about 120 kcal.
The formula behind it
Fat provides 9 kcal per gram (the Atwater factor). A daily target is usually set as a share of calories: fat (g) = (total calories × fat %) ÷ 9. The WHO recommends total fat at 15–30% of energy for adults, with saturated fat below 10%, while the US Dietary Guidelines and most sports-nutrition guidance allow up to 35% total fat. For a 2,000 kcal diet at 30% fat, that is (2,000 × 0.30) ÷ 9 = 67 g of fat a day, of which saturated fat should stay under (2,000 × 0.10) ÷ 9 = 22 g.
Worked example — a 70 kg woman, maintenance about 2,000 kcal a day, cutting at 1,700 kcal (a 300 kcal deficit, above the 1,200 kcal floor for women). At 30% fat, her target is (1,700 × 0.30) ÷ 9 = 57 g of fat a day, with saturated fat under (1,700 × 0.10) ÷ 9 = 19 g. A day that hits it might be: olive oil for cooking (14 g), a handful of almonds (15 g), salmon at dinner (13 g) and the small amounts in yoghurt, eggs and oats (15 g). If she swaps the almonds for a buttered croissant, saturated fat jumps by roughly 10 g and total fat barely changes — the calories are the same, but the fat profile is much worse.
Your plan, step by step
- Work out your calorie target first, then set fat at 25–35% of it — never set fat in grams before you know the calories.
- Count saturated fat separately for a week: butter, cheese, fatty meat, coconut oil and baked goods are the usual sources.
- Swap, don't just cut: replace butter with olive oil, fatty meat with oily fish or chicken, and biscuits with nuts.
- Measure oil and butter for two weeks — a free pour is often two to three times a tablespoon.
- Eat oily fish (salmon, sardines, mackerel) once or twice a week for EPA and DHA, or talk to a clinician about a supplement if you never eat fish.
How to use this guide
Use the fat target as a budget, not a daily pass-or-fail test: average it over the week, because a single high-fat meal does not undo a good pattern. Check your saturated fat once a month by logging a typical week — if it is over 10% of calories, find the one or two foods driving it and swap them. If your weight is falling at 0.5–1% of body weight a week and your energy is steady, the fat level is working.
Common mistakes
Going very low fat to lose weight faster. Fat below about 15% of calories makes food unsatisfying, risks vitamin and hormone shortfalls, and usually ends in a binge. Keep fat at 25–35% and take the deficit from carbohydrate and total calories instead.
Treating all fat as equal. A gram of fat from olive oil and a gram from butter carry the same calories but opposite effects on blood cholesterol. The type of fat is the decision that matters most for health; the total is the decision that matters most for weight.
Forgetting that 'healthy' fats still have calories. Nuts, avocado and olive oil are genuinely healthy foods, and they are also among the most calorie-dense foods that exist. A handful of nuts is a snack; half a bag is a meal's worth of calories.
What this guide does NOT tell you
Fat recommendations are population guidance from the WHO and national dietary guidelines; individual needs vary with health conditions, medication and genetics. People with raised cholesterol, heart disease, gallbladder disease or a family history of early heart disease should discuss fat targets — especially saturated fat — with a clinician or registered dietitian. This guide does not diagnose or treat any condition, and blood cholesterol responds to the whole diet pattern, not to a single food.
Frequently asked questions
How much fat should I eat per day?
Most adults do well on 20–35% of calories from fat: at 2,000 kcal that is about 44–78 g a day, and at 2,500 kcal about 56–97 g. Within that, keep saturated fat below 10% of calories (under 22 g at 2,000 kcal). Very active people and those on higher-calorie diets need more grams, but the percentages stay similar — the target scales with calories, not with body weight alone.
Is saturated fat really bad for you?
Saturated fat raises LDL cholesterol, and high LDL is a well-established risk factor for heart disease — the WHO's 2023 guidance and most national guidelines agree on keeping it under 10% of calories. The debate is about how much it matters in an otherwise healthy diet, not whether the effect exists. The practical move is not to fear a single food but to keep the pattern in check: butter and cheese occasionally, olive oil and fish routinely.
Are low-fat foods better for weight loss?
Not necessarily. Many low-fat products replace fat with sugar and are no lower in calories, and they are often less filling, so people eat more of them. For fat loss, total calories matter more than fat percentage. A full-fat yoghurt eaten in a sensible portion can be a better choice than a low-fat version with added sugar — check the label, not the claim on the front.
Do I need omega-3 supplements?
If you eat oily fish once or twice a week, probably not. If you never eat fish, a supplement is worth discussing with a clinician, because the body converts plant omega-3 (ALA from flaxseed and walnuts) to EPA and DHA inefficiently — typically under 10%. Vegetarians and vegans are the group most likely to benefit, and algae-based supplements provide EPA and DHA directly.
Does eating fat make you fat?
No — eating more calories than you burn makes you gain fat, whatever the source. Fat is the easiest macronutrient to overeat because it is so calorie-dense (9 kcal/g) and because it is often hidden in sauces, pastries and fried foods, so it gets blamed for what is really a calorie surplus. A diet with adequate fat and a calorie deficit loses fat just as well as a low-fat diet at the same calories.
Estimates only, not medical advice. Minimum safe intakes: 1,200 kcal/day women, 1,500 kcal/day men — consult a healthcare professional before a very-low-calorie diet.