Dietary Fats — Saturated, Unsaturated, and Trans

Fat provides 9 kcal per gram — more than double carbohydrate or protein. It is essential for absorbing fat-soluble vitamins (A, D, E, K), building cell membranes and hormones, and supplying essential fatty acids. Types differ by chemical structure and health effect:

• Saturated fat (fatty meats, butter, cheese, coconut/palm oil): solid at room temperature. The Dietary Guidelines for Americans 2025–2030 say saturated fat should in general not exceed 10% of total daily calories, mainly by significantly limiting highly processed foods. The prior 2020–2025 edition paired the same limit with advice to replace saturated fat with unsaturated fat; the 2025–2030 edition drops that framing, lists olive oil first for cooking with butter or beef tallow as other options, and states that more high-quality research is needed on which fats best support long-term health. Independent trial evidence still favours cutting saturated fat: a Cochrane review of 15 long-term randomised trials found that reducing saturated fat lowered combined cardiovascular events by about 17% (risk ratio 0.83, 95% CI 0.70–0.98), with no clear difference between replacing it with polyunsaturated fat or carbohydrate (Hooper et al. 2020). This module therefore keeps unsaturated fats as the default emphasis.
• Monounsaturated fat (olive oil, avocado, most nuts): a cornerstone of the Mediterranean pattern (see The Mediterranean Diet); associated with favorable cholesterol profiles.
• Polyunsaturated fat (fatty fish, walnuts, seeds, vegetable oils): includes the essential omega-3 and omega-6 fatty acids (see Omega-3 and Omega-6 Essential Fatty Acids).
• Trans fat: largely from partially hydrogenated oils. Industrial trans fat raises LDL and lowers HDL; intake should be as low as possible (artificial trans fat is now banned from the US food supply).

Requirements: the Dietary Reference Intakes set the adult Acceptable Macronutrient Distribution Range (AMDR) for fat at 20–35% of total calories, with linoleic acid (omega-6) at 5–10% and alpha-linolenic acid (omega-3) at 0.6–1.2%; they set no intake for saturated or trans fat, advising both be kept as low as possible while eating a nutritionally adequate diet. Very-low-fat diets risk inadequate fat-soluble vitamin and essential-fatty-acid intake; the priority is fat quality (more unsaturated, less saturated, no trans) rather than simply minimizing total fat.

• 9 kcal/g; needed for fat-soluble vitamin absorption, membranes, hormones.
• Saturated fat ≤10% of calories (DGA 2025–2030; unchanged limit).
• Mono- and polyunsaturated fats favored; PUFA includes essential omega-3/6.
• Industrial trans fat: keep as low as possible (now banned in US food supply).
• AMDR for fat: 20–35% of total calories (n-6 5–10%, n-3 0.6–1.2%).