19.1 Macronutrients, Micronutrients, Fiber, Fluids & Supplements

Energy and the Macronutrients

Three nutrients supply energy, and their caloric densities are the most calculation-relevant facts in nutrition:

Fat supplies more than twice the energy per gram of carbohydrate or protein, which is why fat reduction is the highest-yield lever in weight management counseling. A food label showing 12 grams of fat, 30 grams of carbohydrate, and 5 grams of protein contains (12 × 9) + (30 × 4) + (5 × 4) = 108 + 120 + 20 = 248 kilocalories.

The Acceptable Macronutrient Distribution Ranges (AMDR) for adults are 45 to 65 percent of calories from carbohydrate, 20 to 35 percent from fat, and 10 to 35 percent from protein.

Carbohydrates

Carbohydrates are the body's preferred energy source and the only fuel the brain and red blood cells use readily. Simple carbohydrates (monosaccharides and disaccharides — glucose, fructose, sucrose, lactose) absorb rapidly and raise blood glucose quickly. Complex carbohydrates (starches and fiber) digest slowly and provide sustained energy along with vitamins and minerals. Counseling emphasizes complex sources — whole grains, legumes, vegetables — over added sugars, for which the Dietary Guidelines recommend less than 10 percent of total calories.

Proteins

Protein builds and repairs tissue, forms enzymes, hormones, antibodies, and plasma proteins, and maintains fluid balance and acid-base regulation. It is composed of amino acids, nine of which are essential — the body cannot synthesize them, so they must come from the diet.

• Complete proteins contain all nine essential amino acids in adequate proportion: meat, poultry, fish, eggs, dairy, soy, and quinoa.
• Incomplete proteins lack or are low in one or more: most plant sources, including grains, legumes, nuts, and seeds.
• Complementary proteins combine incomplete sources whose limiting amino acids differ, producing complete protein across the day — rice with beans, hummus with pita, peanut butter on whole wheat bread. They do not need to be eaten in the same meal.

The adult Recommended Dietary Allowance is approximately 0.8 grams per kilogram of body weight per day, increasing with pregnancy, lactation, wound healing, burns, and dialysis.

Fats

Fats supply essential fatty acids, carry the fat-soluble vitamins, cushion organs, and insulate the body.

Cholesterol is a sterol found only in animal products; the body also synthesizes it in the liver. For most patients, saturated and trans fat intake affects serum cholesterol more than dietary cholesterol does.

Fiber

Dietary fiber is the indigestible portion of plant food. It provides no calories and comes in two functional forms:

• Soluble fiber (oats, barley, legumes, apples, citrus, psyllium) forms a gel that slows gastric emptying, blunts postprandial glucose rise, and lowers LDL cholesterol.
• Insoluble fiber (wheat bran, whole grains, vegetable skins, nuts) adds bulk, speeds transit, and prevents constipation and diverticular disease.

Recommended intake is approximately 25 grams daily for adult women and 38 grams for adult men; the Nutrition Facts label uses a Daily Value of 28 grams. Most adults consume roughly half that. Counsel patients to increase fiber gradually and to increase fluid intake at the same time — a rapid increase without fluid causes bloating, cramping, and can worsen constipation or cause obstruction.

Vitamins

Vitamins are organic compounds required in small amounts. The division that governs both dosing and toxicity risk is solubility.

Fat-soluble: A, D, E, K

Stored in the liver and adipose tissue, absorbed with dietary fat, and capable of accumulating to toxic levels with excessive supplementation.

Water-soluble: B complex and C

Not stored in appreciable amounts, excreted in urine, and required regularly.

Folic acid supplementation of 400 micrograms daily before conception and through early pregnancy substantially reduces neural tube defects, which is why it is recommended for all people capable of becoming pregnant rather than only those who are pregnant.

Minerals, Electrolytes, and Fluids

Water is the largest single component of the body — roughly 60 percent of adult body weight — and functions as solvent, transport medium, temperature regulator, and joint lubricant. General adult intake guidance is about 2.7 liters daily for women and 3.7 liters for men from all sources, including food, which supplies roughly 20 percent. Requirements rise with fever, exercise, heat, vomiting, and diarrhea, and are restricted in advanced heart failure, some kidney disease, and dialysis. Older adults are at elevated dehydration risk because thirst sensation declines with age.

Dietary Supplements and Herbs

Under the Dietary Supplement Health and Education Act (DSHEA) of 1994, supplements are regulated as foods, not drugs. The practical consequences are substantial and frequently tested:

• Manufacturers do not need Food and Drug Administration approval for safety or effectiveness before marketing.
• The FDA must demonstrate that a product is unsafe after it reaches the market in order to restrict it.
• Labels may carry structure/function claims ("supports immune health") but may not claim to diagnose, treat, cure, or prevent disease, and must bear a disclaimer.
• Potency and purity vary between manufacturers and between lots.

Supplements have real pharmacologic effects and real interactions:

Ask about supplements explicitly during medication reconciliation, because patients routinely do not consider them medications and will answer "no" to "are you taking any medications?" while taking six supplements daily. Document the product, dose, and frequency, and route interaction concerns to the provider or pharmacist. Surgeons commonly ask patients to stop herbal products one to two weeks before an operation for this reason.