Nutrition

How to think about food#

Nearly everything in this chapter is a footnote to two rules: eat the right amount, and eat mostly real food. The camps that say only calories matter, or only quality matters, are both half right: quality shapes how much you eat, and quantity decides your weight.

Why nutrition is hard to study#

Nutrition is the hardest field in this guide to get right. Most evidence comes from observational studies built on food questionnaires, and people who eat well also tend to exercise more and earn more. Trials that randomize people to a diet for years and count heart attacks or deaths are rare, and some research is funded by the industries it studies. See Reading the evidence.

People also respond differently to the same food. A 2015 study that tracked glucose in 800 people across 46,898 meals found wide variation in responses to identical meals, partly because of gut bacteria. General rules still hold, but the best version is the one you can keep for decades.

Quantity: energy balance#

Your weight over time reflects energy eaten versus energy burned. Because the body adapts as you lose weight, the response is slow: in the NIH model behind modern calculators, about half of the eventual change happens in the first year.

To estimate your needs, enter your age, sex, height, weight, and activity into the free NIH Body Weight Planner, which gives a calorie target for maintenance or a goal weight. Then let the scale correct the estimate: weigh yourself each morning, watch the weekly average, and adjust after a few weeks if the trend is off.

Quality: mostly real food#

Food quality changes how much you eat. In a 2019 inpatient trial, 20 adults spent two weeks each on ultra-processed and unprocessed diets, with meals matched for calories offered, sugar, fat, fiber, and sodium. On the ultra-processed diet they ate 508 more calories a day and gained about 2 pounds (0.9 kg); on the unprocessed diet they lost about the same. Moderate

Protein#

Protein builds and maintains muscle, which matters more every decade (see Muscle, bone, and mobility).

Optimal: about 1.6 g per kilogram of body weight a day (0.73 g per pound) if you strength train, which this guide recommends for everyone, and up to about 2.2 g/kg (1 g per pound), the target Peter Attia's practice uses. For a 170-pound (77 kg) person, 1.6 g/kg is about 123 g a day. If you do not train, 1.2–1.6 g/kg is enough. Spread it over three or four meals.

Guideline minimum: the 2025–2030 Dietary Guidelines set 1.2–1.6 g/kg a day (about 0.55–0.73 g per pound), adjusted to your calorie needs, with protein foods at every meal.

Who needs more#

• People who train. In a meta-analysis of 49 trials, protein added to resistance training increased muscle and strength gains, with no further lean-mass gain above about 1.6 g/kg a day, so 1.6 is the floor to aim for and more is a margin for error. The International Society of Sports Nutrition suggests 1.4–2.0 g/kg for most exercising people. Strong
• Adults over 65. Aim for 1.2–1.6 g/kg, and about 0.4 g/kg at each meal: older muscle responds less, and in a tracer study older men needed 0.40 g/kg in a meal for a full muscle-building response versus 0.24 for young men. Guideline minimum: PROT-AGE and ESPEN advise at least 1.0–1.2 g/kg, and 1.2–1.5 g/kg with acute or chronic illness. Moderate
• People losing weight, including on GLP-1 drugs. See Metabolic health.

Healthy kidneys handle these amounts: across 28 trials in 1,358 healthy adults, higher-protein diets did not change kidney function. Moderate

Good sources#

Plant protein#

You do not need meat to hit these targets, and swapping some animal protein for plants may help. In 131,342 US health professionals, each 3% of calories from plant protein was linked to 10% lower mortality, while animal protein was linked to slightly higher cardiovascular mortality. The links appeared mainly in people with at least one unhealthy habit, and the study is observational. Moderate Vegetarians and vegans should diversify plant proteins to balance amino acids.

Fiber, fats, and carbohydrates#

Fiber#

Optimal: at least 30 g a day, and more if your gut tolerates it. Meta-analyses of 185 cohort studies and 58 trials found that people eating the most fiber had 15–30% lower all-cause and cardiovascular mortality and less coronary disease, stroke, type 2 diabetes, and colorectal cancer than those eating the least. Benefits were largest at 25–29 g a day, and the dose-response curves suggested higher intakes could bring even more; trials confirmed lower weight, blood pressure, and cholesterol. Strong

Guideline minimum: adults are advised to eat 21 to 38 g a day depending on age and sex.

Get it from beans, vegetables, whole fruit, whole grains, nuts, and seeds, and increase it over a few weeks with enough water to avoid bloating.

Psyllium husk is the fiber supplement with the strongest data. Across 28 trials, about 10 g a day lowered LDL cholesterol by about 13 mg/dL (0.33 mmol/L) and also lowered ApoB. Moderate Take medications at a different time of day, since fiber can slow their absorption; see psyllium.

Fats#

The lesson from decades of fat research is that replacement matters. Trials that swapped saturated fat for polyunsaturated vegetable oil cut cardiovascular disease by about 30%, similar to a statin, because the swap lowers LDL cholesterol. Strong Optimal: keep saturated fat under 10% of calories, and near 5–6% if your ApoB or LDL is above target. US guidance differs on how far to go:

Let your own LDL or ApoB decide how strict to be; if it is high, cutting saturated fat is one of the few dietary levers that moves it (see ApoB and LDL).

Olive oil has the best evidence of any fat. In PREDIMED, 7,447 Spanish adults at high cardiovascular risk who ate a Mediterranean diet with extra virgin olive oil had 31% fewer heart attacks, strokes, and cardiovascular deaths than a low-fat control group (28% fewer with nuts). It was republished in 2018 after randomization problems, and the finding held. Strong Canola and soybean oil are reasonable for high-heat cooking.

Omega-3 fats from food. Eat fatty fish such as salmon, sardines, or trout at least twice a week, the FDA's goal of at least 8 ounces of seafood a week. Guideline minimum: the AHA recommends one to two seafood meals a week to lower the risk of heart failure, coronary disease, ischemic stroke, and sudden cardiac death. Moderate Fish oil capsules are a separate question; see Supplements.

Industrial trans fats are essentially gone: manufacturers could not add partially hydrogenated oils to foods after June 18, 2018.

Carbohydrates and blood sugar#

Carbohydrate quality matters more than quantity for most people. The Dietary Guidelines favor fiber-rich whole grains and a sharp cut in refined carbohydrates such as white bread, packaged breakfast foods, and crackers. Whole grains track with lower disease risk; the glycemic index, a lab measure of how fast a food raises glucose, predicts far less.

What healthy glucose looks like. In 153 healthy people wearing continuous glucose monitors (CGMs), average glucose was 98–99 mg/dL (104 over age 60), 96% of the day was spent between 70 and 140 mg/dL, and about 30 minutes a day was above 140. Short spikes after meals are normal. Wellness targets such as "never above 140" are heuristics, not clinical standards; the clinical thresholds are in Metabolic health.

Food order. In 11 adults with type 2 diabetes, eating chicken and vegetables 15 minutes before bread and juice lowered glucose 29%, 37%, and 17% at 30, 60, and 120 minutes compared with the reverse order. Moderate

Acid with starch. Lemon juice with bread lowered the glucose peak by about 30% in a small trial, similar to vinegar. A 2024 trial claiming apple cider vinegar caused weight loss was retracted in 2025. Dilute vinegar to protect your teeth. Weak

Ultra-processed food, sugar, and salt#

Ultra-processed food#

"Ultra-processed" comes from the Nova system, which sorts foods by degree of industrial processing. Ultra-processed products contain ingredients rarely used in kitchens, such as high-fructose corn syrup, hydrogenated oils, and hydrolyzed proteins, or additives such as flavors, colors, emulsifiers, and sweeteners. Scanning the ingredient list for them is the practical test.

A 2024 umbrella review of 45 pooled analyses covering about 9.9 million people rated the evidence convincing for links to cardiovascular death (50% higher), type 2 diabetes, anxiety, and common mental disorders, and highly suggestive for all-cause mortality (21% higher). The data are observational and mostly low quality, but the NIH feeding trial shows a likely mechanism: these foods make it easy to overeat. Moderate

Not all processing is bad: the guidelines count frozen, dried, or canned produce with little added sugar as good options, and plain yogurt and canned beans are nutritious. Target snacks, sweets, sugary drinks, processed meat, and ready meals built from refined starch, sugar, and oil.

Added sugar and sweeteners#

The 2025–2030 Dietary Guidelines say no amount of added sugar is recommended, a meal should contain no more than 10 g, and sugar-sweetened drinks should be avoided. The AHA's limit is 100 calories a day from added sugar for most women (about 6 teaspoons) and 150 for most men (about 9 teaspoons). Sugar in whole fruit and plain milk does not count.

Non-sugar sweeteners are not harmless, not all alike, and still better than a daily soda habit.

• They do not help weight long term. The WHO advises against using them for weight control after finding no long-term benefit for body fat. Negative
• Sucralose and saccharin impaired glucose tolerance in a randomized trial of 120 adults at doses below the acceptable daily intake, through gut bacteria.
• Erythritol, common in "keto" products, was linked to more heart attacks and strokes in people undergoing cardiac evaluation and increased platelet clotting in healthy volunteers; avoid it if you have cardiovascular risk.
• Aspartame is classed by IARC as "possibly carcinogenic" on limited evidence, while WHO and FAO experts kept the acceptable intake at 40 mg/kg a day, about 9 to 14 cans of diet soda for a 154-pound (70 kg) adult.

The guidelines now advise limiting them too. Use diet drinks as a bridge away from sugary ones, not a destination.

Salt and potassium#

Optimal: about 1,500 mg of sodium a day. The 2025 AHA/ACC blood pressure guideline advises under 2,300 mg and ideally approaching 1,500. Lower helps: in the DASH-Sodium trial of 412 adults, going below 2,300 mg lowered pressure more, and the DASH diet plus low sodium lowered systolic pressure by 7 mm Hg in people without hypertension and 11.5 mm Hg in people with it, compared with a typical high-sodium diet. Strong If you sweat heavily in long training or heat, you need more.

Guideline minimum: the Dietary Guidelines set sodium below 2,300 mg a day from age 14.

Potassium pushes the other way. Treat the adequate intake, 3,400 mg for men and 2,600 mg for women, as a floor, and get it from vegetables, beans, potatoes, fruit, and yogurt.

Salt substitutes pull both levers. In a trial of 20,995 older adults in rural China with prior stroke or high blood pressure, a substitute of 75% sodium chloride and 25% potassium chloride lowered stroke by 14% and death by 12% over about five years, without a significant rise in serious high-potassium events. Strong

Meat, fish, eggs, dairy, and plants#

Red and processed meat#

The WHO's cancer agency classifies processed meat (bacon, ham, sausages, deli meats) as Group 1, carcinogenic to humans, based on sufficient evidence for colorectal cancer, and unprocessed red meat as Group 2A, probably carcinogenic. These categories describe how sure the agency is, not how big the risk is, and risk rises with the amount eaten. Keep processed meat occasional. Moderate Unprocessed red meat supplies protein, iron, zinc, and B12 and counts as a protein food in the Dietary Guidelines; choose lean cuts and let fish, poultry, beans, and soy fill most protein days.

Fish and mercury#

The FDA's fish advice cites a goal of at least 8 ounces (about 225 g) of seafood a week on a 2,000-calorie diet. The concern is mercury, which builds up in large predatory fish. The FDA and EPA list these as choices to avoid: king mackerel, marlin, orange roughy, shark, swordfish, tilefish from the Gulf of Mexico, and bigeye tuna. "Best choices" include salmon, sardines, cod, shrimp, freshwater trout, and canned light tuna.

If you are pregnant, breastfeeding, or might become pregnant, the FDA advises two to three 4-ounce servings a week from the best-choices list, and smaller portions for children. If you carry APOE4, the main genetic risk factor for Alzheimer's, observational studies link at least one serving of fatty fish a week to lower risk, while omega-3 supplement trials have not shown clear benefit; see Brain health.

Eggs and dietary cholesterol#

An AHA science advisory published in 2020 found that observational studies generally show no significant link between dietary cholesterol and cardiovascular disease, although trials show higher intakes can modestly raise LDL. If your LDL or ApoB runs high, see how your levels respond.

Dairy#

The biggest change in the 2025–2030 Dietary Guidelines is full-fat dairy: three servings a day on 2,000 calories, with no added sugars. The evidence is mostly observational. In a meta-analysis of 18 studies, higher blood markers of dairy fat were linked to modestly lower cardiovascular risk, though the markers cannot tell cheese from milk from butter. Against that, dairy fat is mostly saturated fat, which raises LDL compared with unsaturated fat, and the AHA's recommended patterns still feature low-fat dairy. Mixed A sensible middle path: favor fermented, unsweetened dairy such as plain yogurt and kefir, and choose lower-fat versions if your LDL or ApoB is high.

Plant-forward eating and legumes#

Every well-supported diet pattern is built mostly from plants. Beans, peas, lentils, nuts, seeds, and soy count as protein foods and bring fiber and potassium that meat lacks. "Plant-based" is not healthy by default: the guidelines warn against highly processed vegan foods and note that vegan diets often fall short in B12, vitamin D, calcium, iron, iodine, zinc, and protein. See nutrient gaps.

What to drink#

Coffee#

An umbrella review of 201 observational meta-analyses found three to four cups a day linked to 17% lower all-cause and 19% lower cardiovascular mortality than none, with less liver disease and some cancers. Pregnancy was the main exception: higher intake was linked to low birth weight and pregnancy loss. Moderate

Brewing matters. Coffee oils called cafestol and kahweol raise LDL cholesterol; a paper filter traps them, so filtered coffee does not affect cholesterol while boiled, French press, and Turkish coffee do.

Caffeine is the limit. The FDA considers 400 mg a day, about two to three 12-ounce cups, not generally harmful for most adults, but sensitivity varies widely; talk to your clinician if you are pregnant or trying to conceive. Caffeine's half-life averages about five hours and is much longer in some people, so stop by early afternoon (see Sleep). The popular rule of waiting 90 minutes after waking has no trial evidence behind it.

Tea#

Brewed green and black tea are good choices. European regulators found catechins from tea generally safe, but green tea extract supplements at 800 mg or more of catechins a day may harm the liver. Drink the tea; skip the extract. Chamomile improved sleep quality in a 2019 meta-analysis of low-quality trials, without improving insomnia itself. Weak

Water and hydration#

The National Academies set adequate total water intake at about 3.7 liters (125 ounces) a day for men and 2.7 liters (91 ounces) for women, roughly a fifth of it from food. For most healthy people, thirst and drinking with meals are enough; you need more in heat and during long exercise.

If you filter your water, choose a filter certified for the contaminants in your local water report; for PFAS, the EPA points to NSF/ANSI 53 or 58 certification. Bottled water is not cleaner: a 2024 analysis found about 240,000 plastic particles per liter, mostly nanoplastics, with unknown health effects. Lead, PFAS, and microplastics are covered in Avoiding harm.

Alcohol#

For health, less is better and none is best; the 2025 blood pressure guideline prefers abstinence. Guideline minimum: the 2025–2030 Dietary Guidelines dropped numeric limits and simply advise drinking less. The evidence is in Avoiding harm.

Meal timing and fasting#

Time-restricted eating#

Time-restricted eating (TRE) means eating within a set window, often 8 to 10 hours. It is a reasonable way to eat less without counting, but trials suggest that is most of what it does. Mixed

• In the TREAT trial of 116 adults, a 16:8 schedule produced no more weight loss over 12 weeks than three structured meals.
• In a 12-month trial of 139 adults with obesity who all cut calories, adding an 8 a.m. to 4 p.m. window made no significant difference.
• In a 2024 feeding study of 41 adults given identical calories, a 10-hour, early window produced the same weight and glucose changes as a late-heavy pattern.

Earlier windows may have a modest metabolic edge: in a small crossover trial in men with prediabetes, eating within six hours and finishing before 3 p.m. improved insulin sensitivity and blood pressure without weight loss. If a window helps you stop evening snacking, use it.

Periodic fasting#

About 12 hours after eating, liver glycogen runs low and the body shifts toward burning fat and making ketones, the "metabolic switch." Fasts of one to three days deepen that shift. Claims that specific benefits begin at a specific hour, such as 36, come from animal and mechanistic work, not human trials. Weak

Fasting-mimicking diets#

A fasting-mimicking diet is a five-day, low-calorie, plant-based meal plan repeated every month or few months. In mice, cycles started in middle age extended lifespan and lowered visceral fat and cancer. In an exploratory analysis of two small human trials, three cycles were associated with lower insulin resistance, less liver fat, and a 2.5-year drop in a biological-age score. The research comes largely from researchers affiliated with the company that sells the kits, and disease outcomes are untested. Weak

Caloric restriction#

Eating less without malnutrition extends life in many animals. The CALERIE trial tested it in 218 healthy, non-obese adults aged 21 to 50. Asked to cut 25%, they managed about 12% for two years, lost 7.5 kg (about 71% of it fat), and improved LDL cholesterol, blood pressure, C-reactive protein, and insulin sensitivity. Restriction also slightly slowed DunedinPACE, one measure of the pace of aging, but not other aging clocks. Moderate Because some of the weight lost is lean tissue, pair any long-term restriction with strength training and enough protein.

Moving after meals#

Muscle contractions pull glucose out of the blood. A meta-analysis of seven crossover trials, mostly in adults with overweight or obesity, found that breaking up sitting with short bouts of standing or light walking lowered post-meal glucose, and ten sit-to-stands every 20 minutes lowered post-breakfast insulin by about 11% in a small trial. Moderate A 10-minute walk after your largest meal is the easy version; see Exercise.

Foods, contaminants, and nutrient gaps#

Foods that pull their weight#

Contaminants in food#

Heavy metals turn up in some healthy foods. The answer is variety and better choices, not fear.

Drinking-water contaminants, microplastics, and other chemicals are covered in Avoiding harm.

Nutrient gaps worth knowing#

A varied diet covers most needs, but a few gaps are common enough to check. Tests are in Blood tests and biomarkers and products in Supplements.

Eating well as you age#

Calorie needs fall with age, but needs for protein, B12, vitamin D, and calcium stay the same or rise, so every bite has to do more work. After 65, aim for 1.2–1.6 g of protein per kilogram a day with about 0.4 g/kg at each meal, well above the 1.0–1.2 g/kg minimum, pair it with resistance training (see Muscle, bone, and mobility), and see your doctor about any unplanned weight loss.

Diets and tools#

Diets at a glance#

Most named diets share a core: mostly plants, little ultra-processed food, enough protein. Pick the one you can keep.

Tools#

• A food log for a few weeks. Cronometer (strong on micronutrients) or MyFitnessPal, once or twice a year, recalibrates your sense of portions, protein, and fiber.
• A scale. Weigh daily, judge weekly averages. Smart scales are compared in Wearables and home monitoring.
• An over-the-counter CGM, briefly. Dexcom's Stelo uses 15-day sensors and costs about $89–$99 a month (2026); Abbott's Lingo uses 14-day sensors. A two-week stint once or twice a year shows which meals and walks change your curve; compare with the healthy norms above. It does not diagnose anything; see Wearables and home monitoring.

Action plan#