A policy mistake that shaped a generation
In 1977, the United States Senate published dietary guidelines recommending that Americans dramatically reduce their fat intake. The food industry responded quickly, replacing fat with sugar and refined carbohydrates to maintain palatability. “Low fat” became synonymous with healthy.
Over the next four decades, obesity rates tripled. Heart disease remained the leading cause of death. The science that the guidelines were based on has since been largely discredited.
Dietary fat was not the problem. The fear of it, and the industrial foods that replaced it, caused far more damage than the fat ever would have.
Why your body cannot function without fat
Fat is not an optional extra. It is a structural and functional requirement for human life. These are not theoretical benefits; they are physiological necessities.
Every single one of the 37 trillion cells in your body has a membrane made primarily of fatty acids. The quality and fluidity of this membrane, which controls everything that passes in and out of the cell, depends directly on the types of fat you eat.
Oestrogen, progesterone, testosterone, and cortisol all require adequate dietary fat for optimal production. Your body can synthesise cholesterol endogenously, but very low fat intake reduces substrate availability and signalling, suppressing sex hormones, causing irregular cycles, low libido, mood disruption, and stalled fat loss.
Vitamins A, D, E, and K cannot be absorbed without dietary fat. These vitamins govern vision, calcium metabolism, antioxidant protection, and blood clotting respectively. Eating salads with fat-free dressing means much of their vitamin content passes through without absorption.
Your brain is approximately 60% fat by dry weight. DHA, an omega-3 fatty acid, makes up a large portion of neuronal membranes. Low omega-3 intake is consistently associated with depression, poor cognitive performance, and increased neuroinflammation. The brain you think with is, quite literally, built from fat.
Fat slows gastric emptying (the rate at which your stomach empties into the small intestine). This creates prolonged feelings of fullness and reduces the frequency of hunger signals. Meals with adequate fat tend to result in lower total calorie intake across the day.
Not all fats are equal
The type of fat matters. Here is a practical breakdown:
Monounsaturated fats
PrioritiseHeart-protective, anti-inflammatory, supports HDL (good) cholesterol. Found in olive oil, avocado, most nuts, and seeds. The backbone of the Mediterranean diet.
Sources: Olive oil, avocado, almonds, cashews, macadamias
Omega-3 polyunsaturated fats
PrioritiseStrongly anti-inflammatory; critical for brain, heart, and eye health. Most people are chronically deficient. EPA and DHA forms (from oily fish) are far more bioavailable than plant ALA (from flaxseed, chia).
Sources: Salmon, mackerel, sardines, herring, trout; walnuts, flaxseed, chia (as ALA)
Saturated fats
ModerateNot inherently harmful in moderate amounts from whole food sources. Excessive intake (especially from processed meat and ultra-processed foods) raises LDL cholesterol. Aim for under 10% of total calories.
Sources: Cheese, butter, coconut oil, red meat, full-fat dairy
Trans fats (partially hydrogenated oils)
MinimiseIndustrially produced trans fats raise LDL and lower HDL simultaneously, which is the worst possible combination for cardiovascular risk. No safe level of intake has been established. Banned in several countries but still present in many ultra-processed foods.
Sources: Fried fast food, many margarines, commercial baked goods, some spreads. Check labels for "partially hydrogenated"
How much fat should you eat?
The scientific consensus for healthy adults is 20-35% of total calories from fat, with a minimum of around 0.5-1 g per kg bodyweight to support hormones.
A critical note on calorie density
Fat contains 9 kcal per gram, more than double the 4 kcal/gram of protein and carbohydrates. Small volumes add up to large calorie totals. One tablespoon of olive oil is 120 kcal. A 30 g handful of almonds is ~180 kcal. This is not a reason to avoid them; it is a reason to measure them. Weigh your oils and nuts until you have an accurate visual reference.
| Context | % calories from fat | At 1,800 kcal |
|---|---|---|
| Minimum (hormone safety floor) | 20% | ~40 g fat/day |
| Fat loss / moderate (typical) | 25% | ~50 g fat/day |
| Balanced / maintenance | 30% | ~60 g fat/day |
| Higher fat approach (e.g. Mediterranean) | 35% | ~70 g fat/day |
6 fat sources worth eating every week
Oily fish (salmon, mackerel, sardines)
The richest dietary source of EPA and DHA omega-3s. Aim for 2-3 portions per week. Associated with reduced depression risk, lower cardiovascular inflammation, and sharper cognition.
Avocado
A whole food rich in monounsaturated oleic acid (the same fat in olive oil), potassium, folate, and fibre. Also comes with 7 g of fibre per avocado, which is rare for a fat source.
Extra virgin olive oil
The cornerstone of the Mediterranean diet. Rich in oleocanthal, a natural anti-inflammatory compound. Use cold on salads for maximum polyphenol benefit; fine to cook at moderate heat.
Walnuts
The nut with the highest omega-3 content (as ALA). Also provides vitamin E, magnesium, and polyphenols. A 30 g handful 4-5 times per week is one of the consistently strongest dietary patterns for brain health.
Eggs (whole)
The yolk contains the majority of the nutrition: choline (critical for liver and brain function), DHA, vitamins A, D and E, plus lutein for eye health. Eggs do not meaningfully raise cardiovascular risk for healthy people.
Chia and flaxseeds
Versatile plant-based omega-3 sources (as ALA). Also gel-forming when wet, creating texture in porridge, yogurt, and smoothies, and significantly slowing glucose absorption of any meal they are added to.
Browse healthy fat recipes in the cookbook to put this into practice.
You now have the complete picture
Over six lessons you have built a complete, evidence-based nutritional framework:
- Lesson 1: Your personalised calorie target and how to get started
- Lesson 2: Energy balance, TDEE, and why the pizza is never the problem
- Lesson 3: Macronutrients: what they are and how to balance them
- Lesson 4: Protein: the macro that does the most work
- Lesson 5: Carbohydrates: fuel without fear
- Lesson 6: Fats: essential, not the enemy
The science does not change. What you do with it, consistently, day after day, is entirely up to you.