Nutrition And Diet

This deck offers a friendly introduction to the fundamentals of nutrition and diet, covering everything from the basics of macronutrients and micronutrients to how calories, food groups, and dietary guidelines like RDA and BMI work together. The cards walk you through what proteins, fats, and carbohydrates actually do in your body, and explore finer distinctions such as simple versus complex carbs, complete versus incomplete proteins, and the role of essential fatty acids. By the end of the deck, you should have a clear, well-rounded picture of how food fuels and supports your health.

It is well suited for students beginning a course in health, biology, or nutrition, as well as anyone who simply wants to make more informed choices about what they eat. If you are studying for an exam, building a personal wellness routine, or just curious about how the body uses food, these cards will give you a solid vocabulary and conceptual foundation to draw on.

Because many of the terms are closely related, try to think about how each new idea connects to the ones you have already learned rather than treating every card in isolation. Spacing your review sessions over several days works especially well for this kind of foundational material, and a quick tip is to bring the concepts into real life as you study, perhaps by looking at a meal and identifying its macronutrients, micronutrients, and fiber content. That small habit can make the definitions stick far more effectively than rote memorization alone.

Nutrition is the science of how food and its components affect the body, encompassing ingestion, digestion, absorption, and utilization of nutrients for growth, maintenance, and repair. At its core are macronutrients (carbohydrates, proteins, and fats), needed in large amounts to provide energy and structural materials, and micronutrients (vitamins and minerals), needed in smaller quantities to regulate metabolism and prevent deficiency diseases. Water, often overlooked, comprises about 60% of body weight and supports digestion, nutrient transport, temperature regulation, and waste elimination; daily needs average 2-3 liters from fluids and food, though excess water in a short period can dangerously dilute blood sodium in a condition called hyponatremia.

The energy content of food is measured in dietary Calories (kilocalories), with carbohydrates and proteins providing 4 kcal/g, fats 9 kcal/g, alcohol 7 kcal/g, and fiber approximately 2 kcal/g. Recommended intakes are guided by the Recommended Dietary Allowance (RDA), which covers the needs of 97-98% of healthy individuals, the Adequate Intake (AI), used when evidence is insufficient for an RDA, and the Tolerable Upper Intake Level (UL), beyond which toxicity risks rise, especially for fat-soluble vitamins and minerals like iron. To interpret body weight status, Body Mass Index (BMI, kg/m²) classifies individuals as underweight (below 18.5), normal (18.5-24.9), overweight (25-29.9), or obese (30 or higher), though it remains only an estimate of body fat. Nutrition labels translate these concepts into practice: serving size, calories, and percent Daily Value (%DV) reveal nutrient density, with under 5% DV indicating low and over 20% DV indicating high content, and ingredients listed by weight from most to least.

The NOVA classification further helps consumers by grouping foods into unprocessed or minimally processed (apples, milk), processed culinary ingredients (oils, salt), processed foods (cheese, bread), and ultra-processed products (sodas, chips). Ultra-processed foods now supply roughly half of calories in many Western diets and are linked to obesity and chronic disease, so limiting them to under 20% of intake is widely recommended. It is also important to distinguish food allergies, which are IgE-mediated immune reactions (such as those to peanuts and shellfish) that can cause anaphylaxis even from trace amounts, from food intolerances, which are non-immune and dose-dependent, as in lactose intolerance caused by lactase deficiency. Together, these frameworks translate nutrition science into everyday food choices.

Carbohydrates are the body's primary energy source at 4 kcal/g, divided into simple sugars that digest quickly for fast energy and complex starches that release glucose more gradually for sustained activity. The glycemic index (GI) ranks how quickly a food raises blood sugar, with low GI (55 or below) like oats preferable for stable energy, while glycemic load (GL) multiplies GI by actual carbohydrate quantity to reflect real-world portions; a watermelon has high GI around 72 but low GL around 5 per typical serving, whereas a bagel has both high. Dietary fiber, an indigestible plant carbohydrate, divides into soluble types (oats, psyllium, beans) that dissolve into a gel to slow gastric emptying, bind bile acids, and lower LDL cholesterol, and insoluble types (wheat bran, vegetables) that add bulk and speed transit to prevent constipation; adults should aim for 25-38 g daily, with attention to fiber's role in promoting short-chain fatty acid production in the colon. Functional fiber, by contrast, is isolated or synthetic (inulin, polydextrose) and added to processed foods to boost fiber content on labels.

Proteins supply 4 kcal/g and are composed of 20 amino acids, nine of which are essential and must come from the diet while others become conditionally essential under stress, illness, or prematurity. A complete protein contains all nine essential amino acids in adequate proportions in a single food (meat, eggs, soy, quinoa), while complementary proteins combine two or more incomplete sources, such as rice and beans, to supply the full set; modern nutrition views daily intake as adequate rather than requiring every meal to be complete. Protein quality is increasingly measured by the Digestible Indispensable Amino Acid Score (DIAAS), which evaluates digestibility at the ileum and can exceed 1.0, replacing the older Protein Digestibility-Corrected Amino Acid Score (PDCAAS) that capped at 1.0. Leucine is the key anabolic signal that activates mTORC1 to trigger muscle protein synthesis, with about 2.5-3 g per meal maximizing this response in younger adults, though older adults often need 30-40 g per meal to overcome anabolic resistance. High-protein diets enhance satiety through GLP-1, CCK, and PYY release while suppressing ghrelin, modestly raising 24-hour energy expenditure via a thermic effect of 20-30%. Gelatin and hydrolyzed collagen peptides, while incomplete proteins lacking tryptophan, may modestly support skin and joint health.

Fats, the most energy-dense macronutrient at 9 kcal/g, include saturated fats (butter, palm oil) that generally raise LDL cholesterol, monounsaturated fats (olive oil, avocado, nuts) that lower LDL while maintaining HDL, and polyunsaturated fats (sunflower oil, fish oil) that lower LDL and supply essential linoleic and alpha-linolenic acids; trans fats should be avoided. Omega-3 fatty acids deserve special mention: ALA from plants must be converted to EPA and DHA, but conversion is less than 10% efficient, so direct sources like fatty fish or algae oil are preferred for the anti-inflammatory and brain-health benefits of EPA and DHA. The liver regulates cholesterol homeostasis by downregulating synthesis when dietary cholesterol rises, though about 25% of people are hyper-responders whose LDL rises more sharply with intake. Plant sterols and stanols, added to margarines and other foods at 2 g/day, can lower LDL by 7-12% by competing with cholesterol for intestinal absorption, and conjugated linoleic acid (CLA) from ruminant fat has modest, isomer-specific effects on body composition.

Vitamins are organic compounds that regulate metabolism, support immunity, and act as antioxidants. The fat-soluble vitamins A, D, E, and K are stored in adipose tissue and liver, so excess intake raises toxicity risk; hypervitaminosis A causes liver damage and birth defects, while excess D leads to hypercalcemia and kidney stones. Vitamin A exists as retinol from animal sources (liver, eggs, dairy) and provitamin carotenoids from plants (carrots, spinach); excess preformed retinol is teratogenic, whereas carotenoid conversion is regulated and safer. Vitamin D is uniquely synthesized when UVB radiation converts 7-dehydrocholesterol in skin to cholecalciferol, then hydroxylated in liver and kidney to active calcitriol; latitude, season, pigmentation, sunscreen use, and age all affect synthesis, and many adults need supplementation to support calcium absorption and prevent rickets or osteomalacia. Vitamin E, found in wheat germ oil, sunflower seeds, and almonds, is a lipid-soluble antioxidant protecting cell membranes at an RDA of 15 mg/day, though high-dose supplements above 400 IU have shown increased mortality risk in meta-analyses.

Vitamin K splits into two functionally distinct forms: K1 (phylloquinone) from leafy greens drives hepatic clotting factor synthesis, while K2 (menaquinone) from fermented foods, egg yolks, and gut bacteria activates extrahepatic proteins like osteocalcin and matrix Gla-protein, directing calcium into bone and away from arteries. Water-soluble vitamins, including the B-complex and C, are not stored but excreted in urine, making daily intake important. Folate is critical for DNA synthesis and methylation, with deficiency in early pregnancy (days 21-28 of gestation) causing neural tube defects such as spina bifida, which is why the RDA rises to 600 µg/day in pregnancy and folic acid supplementation is routinely recommended. Vitamin B12 deficiency causes megaloblastic anemia, neuropathy, and cognitive decline, especially in vegans, the elderly, and users of metformin or proton pump inhibitors. Biotin (B7) is a coenzyme for carboxylases, and its deficiency causes dermatitis, alopecia, and lethargy, though it can interfere with lab tests for troponin and thyroid function, an important clinical caveat. Choline, found abundantly in eggs and liver, supports cell membranes, acetylcholine synthesis, and methylation, with AI of 425 mg/day for women and 550 mg/day for men.

Among minerals, calcium builds bone and teeth, supports muscle contraction and nerve signaling, and pairs with vitamin D for absorption; dairy and leafy greens are top sources, though large calcium doses (>300 mg) taken with iron-rich foods inhibit iron absorption and should be spaced by two or more hours. Iron exists as heme (from animal sources, 15-35% absorption, enhanced by meat factor) and non-heme (from plants, 2-20% absorption, enhanced by vitamin C but inhibited by phytates, tannins, polyphenols, and calcium); the body regulates iron via hepcidin, which rises with repletion or inflammation to sequester iron in macrophages. Magnesium is a cofactor in over 300 enzymatic reactions, with pumpkin seeds, spinach, and almonds as leading sources; deficiency contributes to insomnia, cramps, hypertension, and type 2 diabetes. Iodine, essential for thyroid hormone synthesis, comes mainly from iodized salt, seaweed, and dairy, with needs rising in pregnancy (220-250 µg/day) to support fetal neurodevelopment. Zinc supports immunity and wound healing through thymulin activity and T-cell maturation, though phytates in plants bind zinc and reduce its bioavailability, particularly relevant in vegetarian diets. Selenium, incorporated into selenoproteins including glutathione peroxidase, is found richly in Brazil nuts (one nut contains roughly 68 µg) and protects against oxidative damage, with an UL of 400 µg/day.

Daily energy expenditure rests on three components: basal metabolic rate (BMR), which accounts for 60-75% and represents calories burned at rest for vital functions, calculated by the Harris-Benedict equation factoring age, sex, weight, and height; diet-induced thermogenesis (DIT) or the thermic effect of food, representing energy used to digest and process nutrients and highest for protein at 20-30%, followed by carbohydrates (5-10%) and fats (0-3%); and physical activity. A high-protein diet can therefore raise 24-hour expenditure by 50-100 kcal/day. Understanding the energy density of foods (alcohol 7 kcal/g, fat 9 kcal/g, carbs and protein 4 kcal/g, fiber around 2 kcal/g) explains why high-fat foods like oils, butter, and nuts deliver more calories per gram than fruits and vegetables. Energy balance compares calories in versus out and determines weight change, while macronutrient balance, the relative proportions of protein, carbs, and fat, influences metabolic health, hormones, and body composition independent of total calories.

Body weight regulation hinges on the distinction between hunger, the physiological drive from ghrelin, glucose, and gastric signals, and appetite, the psychological desire shaped by sight, smell, memory, stress, and social cues. Satiation ends a meal via gastric distension and gut hormones like CCK and GLP-1, whereas satiety suppresses hunger between meals; high-volume, high-protein, high-fiber foods boost both, while hyperpalatable foods undermine satiation. Leptin, secreted by adipocytes in proportion to fat stores, normally signals satiety to the hypothalamus, but in obesity leptin resistance develops so that high circulating levels fail to suppress appetite. The endocannabinoid system, via CB1 receptors, modulates hedonic appetite, which explains why CB1 antagonists like rimonabant produced depression as a side effect, and why THC triggers the so-called munchies for sweet and fatty foods. The protein leverage hypothesis proposes that humans prioritize a fixed absolute protein intake (around 15-20% of energy) and overeat carbs and fats when protein is diluted by processed foods, potentially driving obesity.

Body composition matters as much as weight: brown adipose tissue generates heat via uncoupling protein 1 (UCP1) and can be activated by cold, capsaicin, and catechins, while white adipose tissue stores triglycerides; beige adipocytes can be induced in white fat by exercise and certain foods. Sarcopenic obesity, the combination of low muscle mass and high adiposity common in older adults, requires resistance training paired with adequate protein (1.2-1.5 g/kg/day), vitamin D, and modest calorie restriction to preserve lean mass. At the hormonal level, fasting insulin and the HOMA-IR index estimate insulin resistance; values above roughly 1.9-2.5 suggest metabolic dysfunction that can be improved by weight loss, low-GI eating, exercise, and sleep before type 2 diabetes develops, characterized by chronically elevated glucose and HbA1c at or above 6.5%. Lipid assessment has also evolved: LDL-C measures cholesterol mass inside LDL particles, LDL-P counts particle number, apoB counts all atherogenic particles, and non-HDL cholesterol (total minus HDL) better captures risk in metabolic syndrome and diabetes. HDL itself varies, with larger HDL2 particles being more efficient at reverse cholesterol transport than smaller HDL3 particles, though simply raising HDL-C with drugs has not consistently lowered cardiovascular events.

A balanced diet provides adequate nutrients from all food groups in proper proportions, with MyPlate guidance recommending half the plate from fruits and vegetables, plus whole grains and lean proteins. Among well-studied patterns, the Mediterranean diet emphasizes fruits, vegetables, whole grains, fish, olive oil, and nuts while limiting red meat and sweets, and is consistently linked to lower cardiovascular disease and greater longevity. The DASH diet similarly reduces sodium and boosts potassium-rich produce, whole grains, and low-fat dairy, lowering systolic blood pressure by 8-14 mmHg in hypertensives and offering an effect comparable to a single antihypertensive medication, especially when sodium falls below 1500 mg/day. The MIND diet combines Mediterranean and DASH principles with specific brain-healthy foods like leafy greens, berries, nuts, and fish, with cohort studies suggesting a 53% reduction in Alzheimer's risk with strict adherence, though randomized trial evidence remains limited.

Plant-based diets span a spectrum: vegans exclude all animal products and must plan for B12, calcium, iron, omega-3, and zinc; vegetarians (lacto-ovo) include dairy and eggs; pescatarians add fish and seafood. Each lowers cardiovascular risk when well-planned. By contrast, the paleo diet excludes grains, legumes, and dairy, often leading to calcium and vitamin D shortfalls, while the carnivore diet goes further to exclude all plants, risking fiber, vitamin C, vitamin K1, magnesium, and phytochemical deficits over time. The ketogenic diet (under 50 g carbohydrate/day) shifts the body into ketosis within 3-7 days, with the brain eventually deriving roughly 70% of energy from ketones; full keto-adaptation takes 2-6 weeks and is aided by electrolyte repletion. Other named approaches include the four-phase Dukan diet, intermittent fasting and time-restricted eating (which confine intake to 8-10 hour windows or cycle fasting and feeding periods), and the alkaline diet, which falsely claims that food pH alters blood pH, a tightly regulated value around 7.4 regardless of intake. Free sugars, defined as sugars added by manufacturers or present in honey, syrups, juices, and concentrates, are targeted by policy (such as the UK sugar tax) and the WHO because they drive energy overconsumption without satiety.

Therapeutic nutrition tailors patterns to disease. For diabetes, low-GI carbs, fiber, lean proteins, and healthy fats stabilize blood sugar while refined sugars and large portions are limited, with type 1 management centering on carb counting and insulin timing and type 2 emphasizing weight loss and reduced refined carbohydrates. Hypertension responds to sodium restriction (<2300 mg/day, ideally 1500 mg), potassium increases (3500-4700 mg from produce), and weight loss. Heart-healthy approaches, including DASH and Mediterranean patterns, lower LDL and triglycerides while replacing saturated fat with monounsaturated and polyunsaturated sources. NAFLD management relies on 7-10% weight loss, Mediterranean or low-carb patterns, abstention from alcohol, and regular exercise, with coffee consumption (two or more cups/day) associated with reduced fibrosis progression. Gout benefits from reducing purine-rich foods and fructose while increasing low-fat dairy and water; vitamin C supplementation (500 mg/day) modestly lowers urate. PCOS responds to low-GI eating, adequate protein, omega-3 fats, and 5-10% weight loss to restore ovulation, with myo-inositol (4 g/day) showing promise for insulin sensitivity. Hypothyroidism requires adequate but not excessive iodine, plus selenium and zinc, while avoiding soy, calcium, and iron within four hours of levothyroxine. Celiac disease demands strict, lifelong gluten avoidance (wheat, barley, rye, and cross-contaminated oats) with screening for iron, calcium, B12, and folate. SIBO and IBS often respond to low-FODMAP diets that limit fermentable oligosaccharides, disaccharides, monosaccharides, and polyols—lactose, excess fructose, fructans, GOS, and polyols—to reduce bloating and pain. GERD benefits from avoiding trigger foods, eating smaller meals, and elevating the head of bed. CKD requires sodium, potassium, and phosphorus restriction in later stages, with protein moderated to 0.6-0.8 g/kg/day and adequate calories to prevent catabolism.

Malnutrition arises from undernutrition, overnutrition, or imbalances and may lead to stunting, obesity, or specific deficiency syndromes; the short-term BRAT diet (bananas, rice, applesauce, toast) is no longer recommended beyond 24-48 hours for acute diarrhea, with oral rehydration now preferred. Refeeding syndrome is a critical risk when severely malnourished patients (anorexia, chronic alcoholism, post-bariatric) are refed too quickly; insulin surges drive phosphate, potassium, and magnesium into cells, causing hypophosphatemia, cardiac failure, and rhabdomyolysis, so refeeding must start at 5-10 kcal/kg/day with thiamine and electrolyte monitoring. Hypertriglyceridemia is best managed by reducing added sugars and refined carbs, increasing omega-3s (or 2-4 g/day EPA/DHA under medical guidance), limiting alcohol, and replacing saturated fat with unsaturated sources; severe elevations above 500 mg/dL require low-fat diets to prevent pancreatitis. Reverse dieting, used by physique competitors and chronic dieters, gradually raises caloric intake by 50-100 kcal/week after prolonged restriction to restore metabolism without rapid fat regain, though benefits over intuitive eating remain contested.

The gut microbiome, comprising trillions of microbes, profoundly influences digestion, immunity, and even mood. Prebiotics, including selectively fermented substrates like inulin, FOS, GOS, and resistant starch, feed beneficial bacteria, while probiotics introduce live strains such as Lactobacillus, Bifidobacterium, and Saccharomyces boulardii. Together as synbiotics, they enhance short-chain fatty acid (SCFA) production, especially butyrate, which fuels colonocytes and reduces inflammation, propionate, which supports hepatic gluconeogenesis, and acetate, which contributes to lipogenesis. Resistant starch, found in cooled cooked potatoes, green bananas, and legumes, escapes small intestinal digestion and ferments in the colon to produce these SCFAs. Dysbiosis has been linked to obesity, irritable bowel syndrome, and even neuropsychiatric conditions via the gut-brain axis, while polyphenols from berries, cocoa, green tea, and olive oil modulate microbial composition and yield metabolites that cross the blood-brain barrier to influence neuroinflammation and synaptic plasticity. Gut microbes also convert dietary choline and L-carnitine from red meat and eggs into trimethylamine (TMA), which the liver oxidizes to TMAO, a compound associated with atherosclerosis.

Polyphenols, plant compounds like flavonoids, resveratrol, anthocyanins, and catechins, exert antioxidant and signaling effects despite low bioavailability (often under 10%); gut microbes metabolize them into active forms. Coffee's chlorogenic acids improve insulin sensitivity and hepatic glucose metabolism, and habitual intake (3-5 cups/day) is linked to lower risk of type 2 diabetes, Parkinson's, and liver disease, with unfiltered coffee raising LDL via cafestol. Polyphenols also support cardiovascular health by improving endothelial nitric oxide bioavailability and reducing LDL oxidation. Antioxidants like vitamins C and E and beta-carotene neutralize free radicals to prevent cellular damage, and anti-inflammatory diets rich in omega-3s and polyphenols reduce chronic inflammation, measurable via CRP, IL-6, and TNF-α and linked to arthritis, cancer, and cardiovascular disease. Pro-inflammatory patterns heavy in trans fats, refined sugar, and processed meat drive the opposite pattern, which the Dietary Inflammatory Index attempts to quantify.

For athletes and active individuals, performance nutrition layers on additional principles. Carbohydrate needs rise to 6-10 g/kg daily for fuel, with protein at 1.2-2 g/kg to support repair, and strategic timing: a carb-focused meal 2-3 hours pre-workout, optional fast-fuel snacks 30-60 minutes before, and carbs plus protein within the recovery window. Leucine thresholds of 2.5-3 g per meal maximize muscle protein synthesis, and spreading protein across three to four feedings is more anabolic than a single bolus, while meal frequency itself does not stoke metabolism beyond the thermic effect of the same total calories. Caffeine at 3-6 mg/kg is ergogenic, increasing adrenaline, fat oxidation, and alertness without significant diuresis in habitual users, though doses above 400 mg/day (200 mg in pregnancy) raise adverse-event risk. Beetroot juice's dietary nitrates convert to nitric oxide, improving vasodilation and time-trial performance with effects peaking 2-3 hours after ingestion. Endurance athletes carb-load at 8-12 g/kg/day for 2-3 days pre-event and consume 30-60 g/hour during exercise exceeding 90 minutes to spare muscle glycogen and delay fatigue. Adequate electrolytes, including sodium, potassium, chloride, magnesium, calcium, and phosphate, are essential for nerve impulses and muscle contraction, with bananas, potatoes, beans, nuts, and dark chocolate providing major cations.

Beyond diet itself, sleep exerts a powerful influence: poor sleep disrupts ghrelin and leptin, increasing appetite for energy-dense foods and impairing the glymphatic system that clears brain metabolites like β-amyloid during rest; diets high in saturated fat and alcohol suppress glymphatic function, while omega-3s and fasting-mimicking patterns may support it. Personalized nutrition is an emerging field that tailors macronutrient targets and identifies allergens using genetics, microbiome, and lifestyle data, while epigenetics research shows that dietary factors like folate influence DNA methylation and gene expression without altering the underlying sequence. Alcohol provides 7 kcal/g of empty calories, displaces nutrient-dense foods, impairs absorption of thiamine, folate, B12, and zinc, and contributes to liver disease over time. Across all of these themes, whole-food choices consistently outperform supplements and isolates, illustrating that combinations of nutrients in their natural matrices deliver synergies (vitamin C boosting iron absorption, fat aiding fat-soluble vitamin uptake) that no single compound can replicate.