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 recommend limiting it to less than 10% of total calories and replacing it with unsaturated fat to support heart health.
• Monounsaturated fat (olive oil, avocado, most nuts): a cornerstone of the Mediterranean pattern (see 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-3-6).
• 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 Acceptable Macronutrient Distribution Range for fat is 20–35% of total calories. 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 (replace with unsaturated).
• 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.

• omega-3-6 — the essential polyunsaturated fats.
• reducing-dietary-fat — historic emphasis on cutting total fat.
• mediterranean-diet — pattern rich in unsaturated fat.
• processed-foods — common source of saturated/trans fat.