Dietary fats have been the subject of intense debate for decades. Once widely regarded as the main drivers of cardiovascular disease and obesity, fats were systematically reduced or removed from many diets. However, more recent evidence reveals that the health effects of fat depend heavily on its type, source, and the overall dietary pattern in which it is consumed.

Fats are indispensable to human physiology. They form the structural basis of cell membranes, act as carriers for fat-soluble vitamins (A, D, E, and K), provide a concentrated energy source, and influence hormonal and metabolic regulation. Their biological effects vary considerably, and individual health status can alter how different fats are processed and utilised.

The brain itself is approximately 60% fat by dry weight, with omega-3 DHA playing a critical role in neural function. Beyond the brain, dietary fats influence gut microbiota composition, which affects metabolic and immune health. Even intramuscular fat provides quick energy during endurance exercise.

The “low-fat” movement of the late 20th century often replaced fat with refined carbohydrates and added sugars to maintain palatability in processed foods—a shift now understood to have contributed to worsening metabolic health rather than improving it.

Broad statements such as “all fat is bad” or “low-fat is always best” oversimplify a far more complex picture.

What Exactly Are Fats?

From a nutritional perspective, fats — also known as lipids — are organic molecules composed of carbon, hydrogen, and oxygen. They are the most energy-dense macronutrient, providing approximately 9 kcal per gram — more than double the energy provided by protein or carbohydrate.

However, fats are not merely a fuel source. They play critical physiological roles, including:

Structural integrity – forming an essential component of every cell membrane
Nutrient absorption – enabling uptake of fat-soluble vitamins A, D, E, and K
Protection – cushioning and insulating organs
Thermoregulation – maintaining stable body temperature
Hormone synthesis – supporting production of steroid hormones such as oestrogen, testosterone, and cortisol
Metabolic signalling – influencing appetite regulation, insulin sensitivity, and energy expenditure through hormone-like messengers

Importantly, adipose tissue is not an inert storage depot. It functions as a metabolically active endocrine organ, releasing signalling molecules that communicate with the brain, liver, muscles, and immune system — affecting everything from hunger to inflammation.

Types of Fat

The chemical structure and dietary source of a fat determine how it behaves in the body and influences health.

Saturated fats
Typically solid at room temperature. Predominantly found in animal-derived foods such as meat, butter, cheese, and cream, as well as certain plant sources like coconut and palm oil. Some saturated fatty acids can raise LDL cholesterol in susceptible individuals, though effects vary by type. For example, stearic acid (abundant in beef and cocoa) appears neutral on blood cholesterol.
Monounsaturated fats (MUFA)
Usually liquid at room temperature. Present in olive oil, avocados, almonds, cashews, and sesame seeds. Associated with improved cardiovascular outcomes, reduced inflammation, and enhanced blood glucose regulation.
Polyunsaturated fats (PUFA)
Includes essential omega-3 and omega-6 fatty acids, which must be obtained through diet. Omega-3s (oily fish, flaxseed, chia, walnuts) are critical for brain development, mood, and cardiovascular function. Omega-6s (sunflower oil, many nuts and seeds) are essential but excessive intake from processed sources may contribute to pro-inflammatory states if not balanced with omega-3s.
Trans fats
Found mainly in partially hydrogenated oils and many processed foods. Strongly linked to increased cardiovascular risk; guidelines recommend minimising or eliminating intake.

Fat as a Living Organ

Body fat is often perceived as static “padding,” but adipose tissue is metabolically active. It stores energy and produces hormones such as:

Leptin – signals satiety to the brain
Adiponectin – regulates blood sugar and has anti-inflammatory effects

When fat cells become overfilled and inflamed, these signals can be disrupted, potentially leading to insulin resistance, increased hunger, and fatigue.

Types of Body Fat

Adipose tissue is metabolically diverse, with distinct types serving different physiological roles:

White adipose tissue (WAT) stores energy in large lipid droplets, provides insulation and cushioning, and serves as a calorie reservoir. Excess white fat accumulation associates with obesity and metabolic disease.
Brown adipose tissue (BAT) is rich in mitochondria, containing iron that imparts its darker colour. Brown fat burns calories through non-shivering thermogenesis, generating heat and increasing energy expenditure.

Humans have more brown fat at birth, especially around the neck and upper back, which helps newborns maintain body temperature. Brown fat declines with age but can be stimulated by cold exposure and hormones like norepinephrine. White fat can also partially convert into metabolically active “beige” fat with some thermogenic capacity under stimuli such as cold or exercise.

**Salmon & walnut salad with roasted sweet potato:** A nutrient-packed meal rich in omega-3 healthy fats, fibre, and antioxidants that support hormone balance, gut health, and sustained energy.

Why Source Matters More Than Quantity

Earlier dietary guidelines focused on total fat reduction. However, evidence increasingly shows that fat type and source are crucial for health.

Whole-food fat sources like extra-virgin olive oil, nuts, seeds (pumpkin, sunflower, flax, chia, sesame, shelled hemp), nut butters, oily fish, and avocados provide beneficial fatty acids alongside fibre, antioxidants, polyphenols, vitamins, and minerals. For example, olive oil enhances absorption of fat-soluble plant compounds like beta-carotene.
Processed fat sources including highly refined vegetable oils, deep-fried foods, and many packaged snacks may contain oxidised or damaged fats and often have an imbalanced omega-6 to omega-3 ratio, potentially contributing to systemic inflammation and adverse metabolic effects.

Top 10 Sources of Healthy Fats

Extra Virgin Olive Oil — rich in monounsaturated fats and antioxidants, supports heart and metabolic health.
Avocados — high in monounsaturated fats, fibre, and potassium; promotes satiety and heart health.
Nuts (Almonds, Walnuts, Cashews) — balanced mono- and polyunsaturated fats, protein, and fibre.
Seeds (Chia, Flax, Pumpkin, Sesame) — rich in omega-3s, fibre, and minerals.
Oily Fish (Salmon, Mackerel, Sardines) — excellent EPA and DHA omega-3 source for brain and heart health.
Nut Butters (Almond, Peanut, Tahini) — concentrated healthy fats and protein; choose natural unsweetened versions.
Coconut Oil — medium-chain triglycerides with unique metabolic effects; use in moderation.
Dark Chocolate (70% cacao or higher) — contains healthy fats, antioxidants, and minerals; enjoy in moderation.
Full-Fat Dairy (Yoghurt, Cheese) — provides saturated and monounsaturated fats, calcium, and probiotics; quality and portion control important.
Eggs — contain beneficial fats, including omega-3 enriched types, plus nutrients like choline.

How Much Fat Do You Need?

UK guidelines recommend around 35% of daily calories from fat, with saturated fat below 11%. Individual needs depend on:

Activity level
Health status and goals
Overall diet quality

Health Considerations and Personalisation

Individual factors such as cardiovascular disease, elevated LDL cholesterol or triglycerides, metabolic syndrome, and genetics affect how fats impact health. Personalised dietary advice focusing on fat quality, quantity, and context is important for these groups. Collaboration with healthcare professionals supports optimal metabolic health and disease management.

🛑 Myth-Busting: Common Fat Misconceptions 🛑

Myth 1: “Eating fat makes you fat.”
Reality: Weight gain results primarily from a sustained positive energy balance regardless of macronutrient source. Healthy fats in nuts, seeds, olive oil, and avocados promote satiety, support hormone balance, and enhance metabolism. Moderate intake of quality fats within a balanced diet may support weight management.

Myth 2: “All saturated fat is bad.”
Reality: Effects vary by fatty acid type, food source, and diet context. Saturated fats from minimally processed foods like dairy, dark chocolate, and coconut differ metabolically from those in processed meats. Individuals with cardiovascular disease or dyslipidaemia should personalise intake under professional guidance.

Myth 3: “Seed oils are always unhealthy.”
Reality: Cold-pressed seed oils provide essential unsaturated fats and antioxidants. Highly refined seed oils in processed foods may oxidise and degrade with high-heat cooking. While omega-6 inflammation links lack strong human evidence, prioritising fresh, quality oils within whole-food diets is advisable.

Myth 4: “Low-fat diets are best for heart health.”
Reality: Eliminating or severely reducing fat is not cardioprotective. Replacement with refined carbs and sugars often worsens glycaemic and lipid profiles. Diets rich in unsaturated fats support cardiovascular health better than restrictive low-fat approaches.

Guiding principles

🎯 Prioritise a variety of fat types, not just total amount.

🥦 Emphasise whole-food sources rich in beneficial fats and micronutrients.

⚠️ Minimise trans fats and limit highly processed oils.

Simple Fat-Friendly Habits

🫒 Use extra virgin olive oil for salads, drizzling, and gentle cooking.

🐟 Eat oily fish twice weekly for omega-3s.

🌰 Include nuts or seeds daily in meals such as porridge, salads, or yoghurt.

🥗 Combine fats with protein and fibre for stable blood sugar and sustained energy.

🚫 Limit deep-fried and ultra-processed foods to occasional treats.

Disclaimer

Content by Jane Lawson is for informational purposes only and is not intended to diagnose, treat, cure, or prevent medical conditions. Always consult your GP or qualified healthcare professional before making changes to your diet or health plan.