Fats

Fat is one of three macronutrients your body needs in large quantities. It’s not just fuel — fat builds every cell membrane in your body, forms the raw material for hormones (testosterone, estrogen, cortisol), insulates your nervous system, and serves as the primary energy store.

The decades-long idea that eating fat makes you fat was wrong. What matters is the type of fat, how it’s processed, what you cook it with, and the balance between different fatty acid families.

Key takeaways

• Saturated fat is stable for cooking — butter, ghee, tallow, and lard withstand high heat without producing harmful oxidation products
• Olive oil is among the best daily fats — the polyphenols in extra virgin olive oil have anti-inflammatory properties; use it raw or at moderate heat
• Omega-3 to omega-6 balance matters more than total fat — modern diets are roughly 15–20:1 omega-6 to omega-3; aim closer to 2–4:1 by eating fatty fish and reducing seed oil use
• Alpha-linolenic acid (ALA) from plants barely converts to EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — only about 5–10% converts in most people; marine sources (fish or algae) are needed for meaningful omega-3 benefit
• Dietary cholesterol is less important than most people think — the liver adjusts its own production in most people; trans fats and refined carbs are more strongly associated with unfavorable LDL changes than eggs
• Fat-soluble vitamins need fat to absorb — taking vitamin D or eating salads without fat means the body absorbs a fraction of what’s available
• Low-fat diets can suppress hormones — testosterone, estrogen, and cortisol are built from cholesterol; consistently eating under 20% of calories from fat is associated with lower hormone levels in some individuals
• Keto is a tool, not the default — ketosis works for specific goals (epilepsy, short-term fat loss, metabolic reset) but limits high-intensity performance and is hard to sustain long-term
• Aim for 25–40% of calories from fat — prioritize omega-3 (EPA/DHA), monounsaturated fat (olive oil), and whole-food saturated fat; minimize seed oils for cooking
• Bile needs time to refill — spacing meals 3–4 hours apart and avoiding snacking lets the gallbladder reload for proper fat digestion

Types of dietary fat

Saturated fat

All carbon bonds are fully occupied by hydrogen atoms — no double bonds. This makes the molecule straight and rigid, which is why saturated fats are solid at room temperature (butter, lard, coconut oil).

Sources: butter, ghee, beef tallow, pork lard, coconut oil, dairy fat, red meat, eggs

What the evidence says: The relationship between saturated fat and heart disease is more complex than the old “saturated fat = bad” narrative. Some meta-analyses of observational data suggest replacing saturated fat with polyunsaturated fat is associated with lower cardiovascular risk. However, a 2025 systematic review of 9 RCTs (n=13,532) found no significant differences in cardiovascular mortality, all-cause mortality, or myocardial infarction between saturated fat reduction and control groups — the strongest trial evidence to date shows null results. Replacing saturated fat with refined carbohydrates and sugar makes things worse. Context matters — but the “whole foods matrix” hypothesis, while plausible, lacks strong direct evidence.

Cooking: Most stable at high heat. Butter, ghee, tallow, and lard resist oxidation better than any unsaturated oil because there are no double bonds to break.

MCTs (medium-chain triglycerides): A subtype of saturated fat with shorter carbon chains (6–12 carbons) found mainly in coconut oil and palm kernel oil. Unlike long-chain fats, MCTs bypass the carnitine shuttle and enter mitochondria directly for oxidation — see the ATP metabolism post for why this matters. MCT oil provides rapid energy from fat but represents a small fraction of total dietary fat intake.

Monounsaturated fat (MUFA)

One double bond in the carbon chain. Liquid at room temperature, semi-solid when cold.

Sources: extra virgin olive oil, avocado, almonds, macadamia nuts, pecans, pork fat (~50% of pork fat is oleic acid — the same MUFA as olive oil)

What the evidence says: Consistently associated with reduced cardiovascular risk, lower inflammation markers, and improved insulin sensitivity. The Mediterranean diet’s benefits are largely attributed to high olive oil intake. Extra virgin olive oil specifically contains polyphenols (oleocanthal, hydroxytyrosol) that inhibit the same inflammatory enzymes as ibuprofen — though at dietary doses the effect is milder and cumulative rather than acute.

Cooking: More stable than commonly believed. Quality EVOO has a smoke point of 175–210°C (350–410°F) — within normal frying range. The USDA classifies olive oil as a “high smoke-point” oil suitable for frying. Its polyphenol content provides antioxidant protection, making it more oxidatively stable than many seed oils at the same temperature. A 2018 study found EVOO retained most antioxidants and was more chemically stable than canola or vegetable oil after heating. Safe for sautéing, pan-frying, and oven roasting; avoid sustained deep-frying above 210°C.

Polyunsaturated fat (PUFA)

Two or more double bonds. The most chemically reactive type — this is important for both biology and cooking.

Two families matter:

Omega-3

• ALA (alpha-linolenic acid) — plant sources: flaxseed, chia seeds, walnuts, hemp seeds. Your body converts ALA to EPA and DHA, but the conversion efficiency is poor: ~5–10% to EPA and less than 1% to DHA. Plant-based omega-3 alone is not sufficient to meet EPA/DHA needs
• EPA (eicosapentaenoic acid) — marine sources: fatty fish (salmon, mackerel, sardines, anchovies), algae. Primary anti-inflammatory omega-3
• DHA (docosahexaenoic acid) — marine sources: same as EPA. Critical for brain structure (makes up ~40% of brain PUFA) and retinal function

Target: 2,000+ mg combined EPA+DHA per day. The klatiPRO supplement stack includes this.

Omega-6

• Linoleic acid (LA) — the dominant omega-6. Sources: seed oils (soybean, sunflower, corn, safflower, canola), nuts, seeds
• Arachidonic acid (AA) — found in meat, eggs, dairy. Precursor to both pro-inflammatory and anti-inflammatory signaling molecules

Omega-6 is not inherently bad — your body needs it. The problem is the ratio.

The omega-6 to omega-3 ratio problem

Humans evolved on a diet with an omega-6 to omega-3 ratio of roughly 1:1 to 2:1. Modern Western diets are 15:1 to 20:1 — sometimes higher.

Why this matters: omega-6 and omega-3 compete for the same enzymes. The traditional view holds that when omega-6 dominates, the body produces more pro-inflammatory signaling molecules. However, 2025 research challenges this: multiple studies including a Framingham Heart Study analysis found that higher blood levels of linoleic acid (the primary omega-6) are associated with lower inflammation biomarkers, not higher. Meta-analyses of controlled trials show increasing linoleic acid intake does not raise inflammatory markers. The ratio still matters for cardiovascular outcomes — a 2024 UK Biobank study (n=85,000+) found higher omega-6:omega-3 ratios associated with 26% higher all-cause mortality — but the mechanism may be omega-3 deficiency rather than omega-6 excess.

How to fix it:

• Increase omega-3: fatty fish 2–3× per week + supplement with EPA/DHA
• Decrease omega-6: reduce seed oil consumption, cook with saturated or monounsaturated fats instead
• You don’t need to eliminate omega-6 — you need to rebalance the ratio

Trans fat

The most dangerous type. Created when hydrogen is forced into unsaturated fat under industrial conditions (partial hydrogenation). This twists the molecule into an unnatural shape your body can’t process properly.

Effects: Increases LDL (bad) cholesterol, decreases HDL (good) cholesterol, increases inflammatory markers, increases cardiovascular mortality. The World Health Organization (WHO) targets global elimination of industrial trans fats.

Where they hide:

• Partially hydrogenated vegetable oils (listed on labels)
• Deep-fried foods (trans fats form during prolonged high-heat frying of unsaturated oils)
• Some margarines and commercial baked goods
• Ultra-processed foods

Small amounts form naturally in ruminant animals (beef, lamb, dairy) as conjugated linoleic acid (CLA). These natural trans fats are structurally different from industrial trans fats and appear to be neutral at the levels found in food — though the evidence base for CLA health effects comes primarily from supplement-dose studies, not dietary intake levels.

Cooking with fat — what to use

This is where most people go wrong. Every oil has a threshold where it starts producing harmful compounds — aldehydes, polar compounds, peroxides, and in some cases, trans fats.

What determines cooking stability

1. Degree of saturation — more saturated = more stable (fewer double bonds to break)
2. Smoke point — the temperature where the oil visibly smokes and rapidly degrades (but damage starts before the smoke point)
3. Antioxidant content — polyphenols and tocopherols (vitamin E) protect against oxidation
4. Free fatty acid content — refined oils have lower free fatty acids but also fewer protective compounds

Cooking guide

Fat	Best for	Avoid
Ghee / clarified butter	High-heat frying, roasting, stir-fry	—
Beef tallow	High-heat frying, roasting	—
Pork lard	Moderate to high heat; roasting, frying	—
Coconut oil (virgin)	Moderate heat; baking, light sautéing	Very high heat (smoke point ~175°C)
Extra virgin olive oil	Moderate heat; sautéing, pan-frying, oven roasting, salads	Sustained deep frying above 210°C
Butter	Low to moderate heat; finishing, baking	High heat (milk solids burn)
Avocado oil (refined)	High-heat cooking (smoke point ~270°C)	Buy from verified sources — quality issues have been documented in commercial products

Use with caution for cooking: soybean oil, sunflower oil, corn oil, canola oil, safflower oil are higher in polyunsaturated fat, which is more susceptible to oxidation at high temperatures than saturated or monounsaturated fats. However, the health concern is primarily about repeated high-heat use and oxidation products — not the oils themselves. Major health institutions (AHA, Johns Hopkins) consider these oils safe and cardiovascular-protective when used appropriately. If cooking with them, keep temperatures moderate, avoid reuse, and keep cooking times short.

The seed oil debate

Seed oils (soybean, sunflower, corn, canola, safflower) are high in linoleic acid (omega-6 PUFA). The debate:

Against seed oils (concerns):

• High omega-6 content shifts the omega-6:omega-3 ratio toward inflammation
• Polyunsaturated fats are chemically unstable — heating produces oxidation products (aldehydes, peroxides)
• Industrial processing (solvent extraction, deodorization, bleaching) strips protective compounds
• Linoleic acid content in body fat has increased dramatically since seed oils became the default cooking fat

In defense of seed oils (counterpoints — supported by 2024-2025 research):

• Replacing saturated fat with polyunsaturated fat is associated with reduced cardiovascular events in observational studies
• Multiple 2025 meta-analyses of controlled trials show increasing linoleic acid intake does not raise inflammatory markers (CRP, IL-6, TNF-α)
• The body tightly regulates LA conversion — only ~0.2% converts to arachidonic acid
• A 2025 study of ~1,900 people found higher blood linoleic acid levels correlated with lower inflammation and better cardiometabolic markers
• AHA, Johns Hopkins, Harvard, and Stanford maintain seed oils are safe and cardiovascular-protective
• The oxidation risk is primarily a cooking problem — cold or moderate-heat use is less concerning

klatiPRO position: the evidence is more nuanced than the anti-seed-oil narrative suggests. For cooking specifically, saturated and monounsaturated fats remain more oxidatively stable at high heat. But unheated seed oils are not the health risk they’re often portrayed as — the 2025 evidence is clear that linoleic acid itself is not pro-inflammatory. The concern is the combination of high heat, oil reuse, and excessive omega-6 at the expense of omega-3 intake.

Cholesterol — dietary vs blood

Eating cholesterol-rich food (eggs, organ meats, shellfish) is associated with smaller increases in blood cholesterol than most people assume.

Why: your liver produces 80% of your blood cholesterol. When you eat more cholesterol, the liver typically compensates by reducing its own production (feedback loop). For most people (~75%), dietary cholesterol has a modest or negligible effect on blood lipid levels.

Hyper-responders (~25% of the population): some people show a meaningful rise in LDL cholesterol when dietary cholesterol intake is high, though the clinical significance depends on particle size and overall risk profile. Genetics (particularly ApoE4 carriers) plays a role. If you eat 3+ eggs daily and your LDL climbs significantly, you may be a hyper-responder — get tested.

Higher-risk populations: a 2025 study in stroke survivors found that each 100 mg/1000 kcal/day increase in dietary cholesterol was associated with 16% higher all-cause mortality and 15% higher cardiovascular mortality. A 2025 umbrella review found egg consumption consistently raises LDL by ~7 mg/dL — modest, but relevant for people with existing cardiometabolic disease. For healthy individuals without CVD risk factors, the same review found “no sufficient quality of evidence to discourage egg consumption.”

What is more strongly associated with unfavorable LDL changes than dietary cholesterol:

• Trans fats (biggest driver)
• Excess refined carbohydrates and sugar (through increased VLDL [very-low-density lipoprotein] production)
• Saturated fat (modest effect, varies by individual)
• Being sedentary

LDL details matter beyond total number: ApoB (apolipoprotein B) — which measures the total atherogenic particle count — is increasingly considered a stronger predictor of cardiovascular risk than LDL-C concentration alone. Small, dense LDL particles are more atherogenic than large, buoyant ones, and a diet high in refined carbs and trans fats tends to shift the pattern toward small dense LDL. A diet high in whole foods, adequate fat, and low sugar tends to produce larger, less harmful particles. If your doctor tests only LDL-C, asking for ApoB provides a more complete picture.

Fat-soluble vitamins

Vitamins A, D, E, and K require dietary fat for absorption. Studies show absorption increases 3–10× when these vitamins are consumed with a fat-containing meal versus without fat.

This is why:

• Vitamin D supplements should be taken with a meal containing fat
• Eating salads with olive oil dressing absorbs more carotenoids (vitamin A precursors) than fat-free dressing
• Fat-free diets can cause deficiencies even when vitamin intake is adequate

See vitamin D for dosing and the D3 + K2 synergy.

Fat and hormones

Fat is the raw material for steroid hormones — testosterone, estrogen, progesterone, cortisol, and DHEA (dehydroepiandrosterone). These are all built from cholesterol, which your body synthesizes from dietary fat.

When total fat intake drops too low (below roughly 20% of calories for extended periods), hormone production can suffer:

• Testosterone may drop in men — a 2021 meta-analysis found very-low-fat diets (under 20% of calories from fat) associated with lower total and free testosterone, though the effect size was modest and based on only 6 studies with 206 total participants. A corrigendum was published in 2026. The finding is directionally consistent but should be considered preliminary until larger RCTs confirm it
• Menstrual irregularities in women — extremely low-fat diets combined with low body fat can disrupt estrogen and progesterone, leading to missed periods (amenorrhea)
• Cortisol dysregulation — cholesterol is the precursor; adequate fat supports normal stress hormone cycling

This doesn’t mean more fat equals more testosterone. There’s a minimum threshold (roughly 20–35% of calories from fat) below which hormone production may be compromised in some individuals. Above that range, additional fat doesn’t continue to raise hormone levels.

Fat digestion

Fat requires a specific digestive process that differs from protein and carbs. See the digestion post for the full mechanism.

The short version:

1. Fat enters the duodenum → triggers cholecystokinin (CCK) release
2. CCK signals the gallbladder to contract and release bile
3. Bile emulsifies fat into tiny droplets (micelles)
4. Pancreatic lipase cuts fat into fatty acids and glycerol
5. Absorbed into intestinal cells, repackaged into chylomicrons, and enter the lymphatic system

This process takes time and requires bile — which is why the protocol spaces meals 3–4 hours apart (the gallbladder needs time to refill) and doesn’t work well with constant snacking.

Ketosis — when fat becomes primary fuel

When carbohydrate intake drops very low (under approximately 50g/day) and glycogen stores deplete, the liver converts fatty acids into ketone bodies — acetoacetate, beta-hydroxybutyrate (BHB), and acetone. These ketones can fuel most tissues, including the brain, which normally runs on glucose.

What happens during ketosis

1. Insulin drops → fat cells release stored fatty acids into the bloodstream
2. The liver converts those fatty acids into ketones
3. Brain, heart, and muscles switch to ketones as primary fuel
4. Over approximately 1–3 weeks the body becomes “fat-adapted” — enzyme systems upregulate to process fat more efficiently

When ketosis has evidence behind it

• Epilepsy — strongest evidence; used clinically since the 1920s to reduce seizure frequency
• Short-term fat loss — appetite suppression from elevated ketones; effective for rapid fat loss phases in adults
• Type 2 diabetes management — can reduce blood sugar and insulin requirements in some individuals (medical supervision required)
• Neurodegenerative conditions — early research suggests possible benefits in Alzheimer’s and Parkinson’s; evidence is preliminary

Limitations

• High-intensity performance may be impaired — sprints, heavy lifts, and HIIT (high-intensity interval training) rely on glycogen, which stays depleted on keto. However, a 2025 meta-analysis found no significant differences in strength or power measures between keto and control diets. The ISSN position (2024) describes effects as “largely neutral or detrimental,” with elite athletes showing more consistent performance decrements
• Adaptation period (“keto flu”) — fatigue, headaches, irritability during the first 1–2 weeks, primarily from electrolyte shifts (sodium, potassium, magnesium). See electrolytes for management
• Difficult to sustain long-term — very restrictive food selection; social eating becomes challenging
• Not suitable for everyone — pregnant or breastfeeding women, people with certain metabolic conditions, and growing adolescents should avoid strict keto without medical guidance

klatiPRO position on keto

Keto is a tool, not the default. The protocol uses moderate fat (roughly 30–40% of calories) with adequate carbs to support training performance. Keto cycling — periods of strict low-carb followed by carb refeeding — is reasonable for specific goals (rapid fat loss, metabolic reset) in healthy adults when combined with proper electrolyte management.

For the carbohydrate perspective on keto, see carbohydrates → how much to eat.

How much fat to eat

For most healthy adults:

• Target: 25–40% of total calories from fat — this supports hormone production, brain function, fat-soluble vitamin absorption, and satiety without excess
• At 2,000 kcal/day → roughly 55–90g fat
• At 2,500 kcal/day → roughly 70–110g fat
• At 3,000 kcal/day → roughly 85–130g fat

Priority order for fat sources:

1. EPA/DHA omega-3: 2,000+ mg/day from fish or supplements — essential for anti-inflammatory balance
2. Monounsaturated fat: daily olive oil, avocados, nuts — best all-around fat for daily use
3. Saturated fat from whole foods: eggs, dairy, meat — stable for cooking, supports hormone production
4. Minimize: seed oils for cooking, industrial trans fats (eliminate entirely)

Practical guidelines

What to eat

• Primary cooking fats: ghee, butter, beef tallow, pork lard (high heat); extra virgin olive oil (moderate heat, finishing)
• Daily olive oil: 2 tablespoons raw extra virgin olive oil (EVOO) per day — polyphenols, oleic acid, anti-inflammatory compounds. Source carefully — some commercial olive oil may be diluted or degraded. Look for harvest date, dark glass, and ideally a polyphenol count on the label
• Omega-3: fatty fish 2–3× per week (salmon, sardines, mackerel, anchovies) + 2,000+ mg EPA/DHA supplement
• Whole food fats: eggs (eat the yolk — that’s where the fat-soluble vitamins and choline are), avocado, nuts (not roasted in seed oils), dark chocolate (85%+)

What to avoid

• Industrial trans fats (partially hydrogenated oils) — eliminate completely

• Seed oils for high-heat cooking — use saturated fats instead

• Margarine (unless confirmed trans-fat-free)

• Deep-fried restaurant food (usually cooked in reused, degraded seed oils)

• “Low-fat” products — they often replace fat with sugar, which is worse

• check klatiCHECK for klati approved sources

---

Research