Sources and References

Primary textbook — Whitney, E., Rolfes, S.R., Crowe, T., Cameron-Smith, D., & Walsh, A. (2019). Understanding Nutrition, 3rd Canadian Edition. Cengage Learning. Online resources — Health Canada, Canada’s Food Guide (food-guide.canada.ca); NIH Office of Dietary Supplements (ods.od.nih.gov); Dietitians of Canada (dietitians.ca)

Chapter 1: The Science and Scope of Human Nutrition

What Is Nutrition and Why Does It Matter?

Nutrition is among the most consequential of biological sciences precisely because it sits at the intersection of chemistry, physiology, behaviour, and public policy. Every human cell depends upon a continuous supply of chemical substrates derived from the foods we eat, and every chronic disease of modern industrialised societies — from type 2 diabetes to cardiovascular disease to certain cancers — has a nutritional dimension that clinicians, researchers, and policy-makers cannot responsibly ignore. For students of kinesiology in particular, understanding nutrition is inseparable from understanding human performance, musculoskeletal integrity, and the trajectory of health across the lifespan.

Nutrients are conventionally divided into six classes: carbohydrates, lipids (fats), proteins, water, vitamins, and minerals. The first three are often called macronutrients because they are required in gram quantities daily and because they collectively supply the chemical energy — measured in kilocalories — that fuels every biological process from ion pumping to voluntary muscle contraction. Vitamins and minerals are micronutrients, required in milligram or microgram amounts, but their physiological functions are no less critical for being quantitatively smaller.

Energy itself is a property of macronutrients that is released through oxidative catabolism. Carbohydrates and proteins each provide approximately \(4 \; \text{kcal g}^{-1}\), while lipids provide \(9 \; \text{kcal g}^{-1}\). Alcohol, though not a nutrient in the strict sense because the body has no requirement for it, supplies \(7 \; \text{kcal g}^{-1}\) and displaces energy-yielding macronutrients in the diets of many individuals.

Dietary Reference Intakes

The Dietary Reference Intakes (DRIs) are a set of reference values established jointly by the Institute of Medicine (now the National Academy of Medicine) in the United States and Health Canada, replacing the older Recommended Nutrient Intakes that had been used in Canada since 1983. The DRIs are not a single number but a family of reference values, each serving a distinct scientific and policy purpose.

A fifth reference value, the Acceptable Macronutrient Distribution Range (AMDR), expresses the proportion of total energy that should come from each macronutrient class. The AMDRs for adults are 45–65% of energy from carbohydrates, 20–35% from fat, and 10–35% from protein. These ranges are set wide enough to accommodate diverse dietary patterns while remaining consistent with reduced risk of chronic disease.

Canada’s Food Guide

Canada’s Food Guide underwent a substantial evidence-based revision in 2019, departing from the earlier food group model and its associated serving-size language in favour of a plate-based visual and qualitative guidance. The 2019 Guide organises foods into three broad categories: vegetables and fruits, whole grain foods, and protein foods. The emphasis on plant-based protein sources — legumes, nuts, and tofu — alongside animal proteins reflects a dual mandate to promote individual health and to acknowledge the environmental sustainability implications of dietary choices.

The Guide also de-emphasises dairy as a separate food group, a change that generated substantial debate among clinicians and the dairy industry, but is consistent with the evidence that the nutritional contributions of dairy products — protein, calcium, vitamin D — can be obtained from other dietary sources. Water is promoted as the beverage of choice, and the Guide devotes considerable attention to the social and contextual dimensions of eating: cooking together, enjoying food, and being aware of food marketing.

Chapter 2: Nutrient Adequacy, Diet Assessment, and Food Labels

Evaluating Dietary Adequacy

Determining whether an individual’s diet is nutritionally adequate requires systematic assessment. Dietary assessment methods range from prospective records (food diaries completed in real time) to retrospective recalls (24-hour dietary recalls) to semi-quantitative food frequency questionnaires. Each method has characteristic strengths and limitations. Prospective records capture actual intake without memory bias but alter eating behaviour through the act of recording. Dietary recalls are less intrusive and can be repeated to capture day-to-day variability, but they depend on memory and portion-size estimation accuracy.

Food composition databases underpin all quantitative dietary assessment. In Canada, the Canadian Nutrient File (CNF) provides compositional data for thousands of foods; in the United States, the USDA FoodData Central database serves the equivalent function. Both databases have limitations: analytic values vary by growing conditions, processing, and preparation methods, and many culturally important foods remain underrepresented.

Reading Food Labels

Canadian food labels are regulated under the Food and Drug Regulations and the Safe Food for Canadians Regulations. The Nutrition Facts table must appear on most packaged foods and lists total calories per serving, as well as the amounts and percent daily values (%DV) for thirteen core nutrients: fat, saturated fat, trans fat, cholesterol, sodium, carbohydrates, fibre, sugars, protein, vitamin A, vitamin C, calcium, and iron. The percent daily value is based on a 2000 kcal reference diet and allows rapid comparison across products.

Ingredient lists appear in descending order by weight, so the first ingredient listed is present in the greatest quantity by mass. Understanding ingredient lists matters because a product may appear low in a nutrient by weight — for example, sugar — while listing three or four different sugar synonyms (sucrose, glucose-fructose, maltose, brown rice syrup) that collectively place sugar near the top of the list.

Nutrition Misinformation

The nutritional information landscape is dense with misinformation, pseudoscience, and commercially motivated distortion. Characteristics of nutrition misinformation include claims that a single food or supplement can cure disease, testimonials substituting for controlled evidence, appeals to naturalistic fallacy, and the deliberate misrepresentation of correlational epidemiology as proof of causality. Critical evaluation of nutritional claims requires an understanding of epidemiological study design — the distinction between randomised controlled trials, prospective cohort studies, and cross-sectional surveys — as well as an appreciation of confounding, effect modification, and publication bias.

Chapter 3: The Digestive System

Overview of Digestion and Absorption

The gastrointestinal tract is a continuous muscular tube approximately nine metres in length from mouth to anus, lined with specialised epithelial cells and associated with accessory organs — salivary glands, liver, gallbladder, and pancreas — that secrete enzymes, bile, and other factors essential to the chemical breakdown of food. The overarching purpose of digestion is to reduce the complex polymers and large molecules found in foods to smaller units that can cross the intestinal epithelium and enter the circulation.

Mechanical digestion begins in the mouth with mastication, which increases the surface area of food particles exposed to enzymatic attack. Salivary amylase initiates starch hydrolysis, though its activity is brief because the acidic environment of the stomach rapidly inactivates it. Swallowing propels the food bolus through the pharynx and oesophagus into the stomach, where it is churned with gastric juice — a mixture of hydrochloric acid (pH 1.5–3.5), pepsinogen (activated to pepsin by the acid), and gastric lipase — to form chyme.

The Small Intestine: The Primary Site of Absorption

The small intestine — duodenum, jejunum, and ileum — is the anatomical site where the great majority of nutrient absorption occurs. Its absorptive surface area is vastly amplified by three anatomical adaptations: circular folds (plicae circulares) that increase surface area roughly threefold, villi (finger-like projections of the mucosa) that increase it further by a factor of ten, and microvilli (the brush border, projecting from the apical surface of each enterocyte) that increase it by a final factor of twenty. In total, the absorptive surface of the small intestine in an adult approaches 200 square metres.

The duodenum receives chyme from the stomach and neutralising bicarbonate from the pancreas, restoring the luminal pH to a range (6–7) suitable for pancreatic enzyme activity. Pancreatic juice contains a battery of hydrolases: pancreatic amylase for starch, pancreatic lipase (with colipase) for triglycerides, trypsinogen and chymotrypsinogen (activated to trypsin and chymotrypsin by enterokinase) for proteins, and ribonuclease and deoxyribonuclease for nucleic acids. Bile, synthesised in the liver and concentrated in the gallbladder, emulsifies fat into small droplets, greatly increasing the surface area accessible to pancreatic lipase.

Absorbed nutrients enter one of two circulations. Water-soluble nutrients — monosaccharides, amino acids, short-chain fatty acids, water-soluble vitamins — enter the hepatic portal vein and travel directly to the liver for processing. Fat-soluble nutrients — long-chain fatty acids, fat-soluble vitamins — are packaged within chylomicrons (lipoprotein particles assembled in enterocytes) and secreted into the intestinal lymphatic system (the lacteals), eventually draining into the thoracic duct and entering the systemic circulation at the subclavian vein, bypassing the liver on first pass.

Chapter 4: Carbohydrates

Structure and Classification

Carbohydrates are organic molecules with the empirical formula \( \left[\text{CH}_2\text{O}\right]_n \), synthesised by photosynthetic organisms from carbon dioxide and water. They exist in a structural continuum from simple monosaccharides through disaccharides and oligosaccharides to complex polysaccharides, and the precise linkage chemistry governing how monomers are joined has profound consequences for digestibility and physiological function.

Dietary fibre comprises the non-digestible polysaccharides and lignins that resist hydrolysis by human digestive enzymes but may be fermented by colonic microbiota. Fibres are classified as soluble (viscous in solution; examples include pectin, beta-glucan, psyllium) or insoluble (cellulose, most hemicelluloses). Soluble fibres reduce postprandial glycaemia by slowing gastric emptying and glucose absorption; they also lower LDL cholesterol through bile acid sequestration. Insoluble fibres promote colonic transit, reducing the duration of contact between luminal contents and the mucosa.

Blood Glucose Regulation

The maintenance of blood glucose within a narrow range — approximately 3.9–6.1 mmol/L fasting — is essential because glucose is the obligate fuel of the central nervous system and the preferred fuel of red blood cells. This homeostasis is achieved through the coordinated actions of two pancreatic hormones: insulin, released by beta cells in response to rising blood glucose, and glucagon, released by alpha cells in response to falling blood glucose.

Insulin promotes glucose uptake by peripheral tissues (primarily skeletal muscle and adipose tissue) via translocation of GLUT4 transporters to the plasma membrane. It simultaneously promotes glycogen synthesis in liver and muscle, and suppresses hepatic glucose output. Glucagon has opposing effects: it promotes hepatic glycogenolysis (breakdown of glycogen to glucose-1-phosphate) and gluconeogenesis (synthesis of new glucose from non-carbohydrate precursors including amino acids, glycerol, and lactate).

The glycaemic index (GI) ranks carbohydrate-containing foods by the blood glucose response they elicit relative to a reference food (glucose or white bread) at equivalent carbohydrate loads. Glycaemic load (GL) adjusts for the amount of carbohydrate actually consumed: \(\text{GL} = \text{GI} \times \text{grams of carbohydrate} / 100\). Both metrics are imperfect predictors of individual glycaemic response, which varies substantially with food matrix, cooking method, meal composition, and host factors including gut microbiome composition.

Chapter 5: Lipids

Classes of Dietary Lipids

Lipids are a heterogeneous class of hydrophobic or amphipathic molecules united by their insolubility in water and solubility in organic solvents. The principal dietary lipids — triglycerides, phospholipids, and sterols — differ substantially in structure, function, and metabolic fate.

Triglycerides (triacylglycerols) constitute approximately 95% of dietary fat and consist of a glycerol backbone esterified to three fatty acid chains. The physical properties and health effects of a triglyceride depend critically on the fatty acid composition. Fatty acids are characterised by chain length and degree of unsaturation. Saturated fatty acids (SFAs) have no double bonds (e.g., palmitic acid, C16:0; stearic acid, C18:0) and are solid at room temperature. Monounsaturated fatty acids (MUFAs) have one double bond (e.g., oleic acid, C18:1n-9, the major fatty acid in olive oil). Polyunsaturated fatty acids (PUFAs) have two or more double bonds and include the essential fatty acids.

Trans fatty acids arise primarily from industrial partial hydrogenation of vegetable oils, a process that converts liquid oils to solid or semi-solid fats by reducing the degree of unsaturation. The hydrogenation process introduces trans double bond geometry (naturally occurring unsaturated fatty acids have cis geometry), and the resulting trans fats raise LDL cholesterol, lower HDL cholesterol, and promote systemic inflammation, making them the dietary lipid most strongly linked to cardiovascular disease risk. In Canada, trans fats have been effectively eliminated from the food supply through regulatory action.

Lipoprotein Transport

Because lipids are water-insoluble, they must be packaged into lipoproteins — spherical particles with a hydrophobic core of triglycerides and cholesterol esters surrounded by a monolayer of phospholipids, free cholesterol, and apolipoproteins — for transport through the aqueous plasma. The major lipoprotein classes differ in size, density, and the direction of lipid transport they mediate.

Chylomicrons transport dietary triglycerides and fat-soluble vitamins from the intestine to peripheral tissues via the lymph and systemic circulation. Very low-density lipoproteins (VLDL) are assembled in the liver and export hepatically synthesised triglycerides to peripheral tissues. As VLDL triglycerides are hydrolysed by lipoprotein lipase in adipose and muscle tissue, the particles are remodelled into intermediate-density lipoproteins (IDL) and then low-density lipoproteins (LDL), which are the primary carriers of cholesterol to cells. High-density lipoproteins (HDL) mediate reverse cholesterol transport, accepting cholesterol from peripheral cells and returning it to the liver for excretion in bile. Elevated LDL cholesterol and low HDL cholesterol are independent cardiovascular risk factors.

Chapter 6: Proteins

Amino Acids and Protein Structure

Proteins are polymers of amino acids joined by peptide bonds, and they serve a staggering diversity of biological functions: as structural components (collagen, keratin), enzymes catalysing metabolic reactions, hormones signalling between tissues, immune antibodies, transport molecules (haemoglobin), and contractile elements (myosin, actin). Twenty standard amino acids are incorporated into human proteins, differing in the chemical character of their side chains.

Protein quality is assessed by the extent to which a food protein provides the essential amino acids in proportions that match human requirements. The Digestible Indispensable Amino Acid Score (DIAAS), recommended by the FAO since 2013, compares the digestible content of each essential amino acid in a food protein to a reference pattern based on human amino acid requirements. DIAAS supersedes the older Protein Digestibility Corrected Amino Acid Score (PDCAAS), which truncated scores at 1.0, obscuring the superior quality of animal-source proteins. Animal proteins (eggs, dairy, meat, fish) generally have DIAAS values above 1.0, while most plant proteins score below 1.0 due to limiting essential amino acids — lysine in grains, methionine in legumes — and lower digestibility.

Protein Metabolism and Requirements

Dietary protein is hydrolysed in the gastrointestinal tract to free amino acids and small peptides, which are absorbed and enter a common metabolic pool from which the body draws for protein synthesis. Protein synthesis and degradation occur continuously and simultaneously — this protein turnover allows the proteome to be remodelled in response to physiological signals without synthesising entirely new proteins from scratch.

The minimum protein requirement is the intake at which protein synthesis balances degradation (nitrogen balance = 0). The current RDA for protein in adults is 0.8 g per kilogram body weight per day, a value that meets the requirements of nearly all sedentary adults. Physically active individuals — particularly those engaged in resistance training or endurance exercise — have elevated requirements, estimated at 1.2–2.0 g/kg/day depending on exercise modality, intensity, and the individual’s training status. Older adults appear to have blunted anabolic responses to dietary protein (anabolic resistance) and may require intakes at the upper end of this range to preserve muscle mass.

Chapter 7: Vitamins

Fat-Soluble Vitamins

The fat-soluble vitamins — A, D, E, and K — share a number of properties arising from their hydrophobicity: they require dietary fat for absorption, they are transported in chylomicrons and lipoproteins, and they can accumulate in adipose tissue and the liver, creating potential for toxicity at high supplemental doses.

Vitamin A encompasses retinol and its precursors, the provitamin A carotenoids (principally beta-carotene). Retinol is essential for visual phototransduction (it forms the chromophore retinal, which isomerises upon absorbing a photon), for immune function, and for the regulation of gene expression through nuclear retinoid receptors that modulate the transcription of genes involved in cell differentiation and proliferation. Night blindness is the earliest clinical manifestation of vitamin A deficiency, progressing to xerophthalmia and corneal ulceration in severe cases.

Vitamin D is unique among vitamins in that it can be synthesised endogenously from 7-dehydrocholesterol in the skin upon exposure to ultraviolet B radiation (wavelength 290–315 nm). Hepatic hydroxylation at carbon 25 produces 25-hydroxyvitamin D (25(OH)D, calcidiol), the major circulating form measured to assess vitamin D status. Renal 1-alpha-hydroxylation converts calcidiol to 1,25-dihydroxyvitamin D (calcitriol), the biologically active hormone. Calcitriol acts via the vitamin D receptor (a nuclear receptor) to promote intestinal calcium and phosphorus absorption, renal calcium reabsorption, and — in concert with parathyroid hormone — bone resorption when serum calcium falls. Vitamin D insufficiency is pervasive in northern latitudes, contributing to suboptimal bone mineralisation and potentially to immune dysregulation.

Vitamin E is a family of tocopherols and tocotrienols; alpha-tocopherol has the highest biological activity. Its primary biochemical function is as a lipid-soluble antioxidant that interrupts lipid peroxidation chain reactions in cellular membranes, protecting polyunsaturated fatty acids from oxidative damage.

Vitamin K comprises phylloquinone (K1, from plant foods) and a family of menaquinones (K2, produced by bacteria and found in fermented foods and animal products). Vitamin K is the essential cofactor for the enzyme gamma-glutamyl carboxylase, which carboxylates glutamate residues in vitamin K-dependent proteins. The most clinically familiar of these are the coagulation factors II (prothrombin), VII, IX, and X, and the anticoagulant proteins C and S, whose activity depends on carboxylation. Osteocalcin and matrix Gla protein, also vitamin K-dependent, are involved in bone mineralisation.

Water-Soluble Vitamins

The eight B vitamins — thiamin, riboflavin, niacin, pantothenic acid, B6, biotin, folate, and B12 — and vitamin C constitute the water-soluble vitamins. These vitamins serve primarily as coenzymes or coenzyme precursors in cellular metabolism, and because they are not stored to any significant extent, deficiency symptoms arise relatively quickly upon dietary inadequacy.

Folate and vitamin B12 are closely linked in the one-carbon transfer reactions that support nucleotide synthesis and DNA methylation. Folate, in its active tetrahydrofolate form, accepts and donates single-carbon units in the synthesis of purines and thymidylate — the latter essential for DNA replication. Vitamin B12 (cobalamin) is required for the remethylation of homocysteine to methionine, a reaction that regenerates active tetrahydrofolate from the methyltetrahydrofolate trap. B12 deficiency thus causes a functional folate deficiency, manifesting as megaloblastic anaemia. B12 deficiency also causes neurological damage — demyelination of the posterior and lateral columns of the spinal cord — through mechanisms involving impaired methylmalonyl-CoA mutase activity rather than folate metabolism. Because B12 is found exclusively in animal-source foods (and fortified products), strict vegans require supplementation.

Chapter 8: Minerals

Macrominerals

The macrominerals — calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulphur — are required in amounts greater than 100 mg per day. Among these, calcium and sodium command particular clinical attention.

Calcium is the most abundant mineral in the body, with approximately 99% residing in the skeleton and teeth as hydroxyapatite \( \left[\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2\right] \). The remaining 1% in blood, extracellular fluid, and soft tissues is physiologically critical: calcium ions participate in muscle contraction, neural transmission, enzyme activation, blood coagulation, and the exocytosis of hormones and neurotransmitters. Serum calcium is tightly regulated by the interplay of parathyroid hormone, calcitriol, and calcitonin, ensuring that circulating concentrations remain at approximately 2.25–2.75 mmol/L regardless of dietary intake. When dietary calcium is insufficient to maintain this concentration, the skeleton is resorbed to supply calcium to the blood — a process that, chronically, reduces bone mass and increases fracture risk.

Sodium is the dominant cation of the extracellular fluid and the primary determinant of extracellular fluid volume and blood pressure. Dietary sodium intake in Canada greatly exceeds recommendations; the estimated average daily intake is approximately 2800 mg, well above the Adequate Intake of 1500 mg for adults. Excess sodium intake is a modifiable contributor to hypertension, which is itself among the strongest risk factors for stroke and cardiovascular disease.

Trace Minerals

Iron is the most prevalent trace mineral deficiency worldwide. Iron exists in two dietary forms: heme iron, found in haemoglobin and myoglobin in meat and fish and absorbed with high efficiency (15–35%), and non-heme iron, found in plant foods and absorbed with much lower efficiency (2–20%) depending on dietary context. Enhancers of non-heme iron absorption include ascorbic acid (which reduces ferric iron to the more soluble ferrous form) and the meat factor (an incompletely characterised component of muscle tissue). Inhibitors include phytates (in whole grains and legumes), polyphenols (in tea and coffee), and calcium.

Zinc is a structural component of over 300 enzymes and transcription factors and is essential for immune function, wound healing, DNA synthesis, and the maintenance of taste acuity. Like non-heme iron, zinc absorption from plant foods is reduced by phytate binding, so vegetarians and vegans have higher requirements.

Chapter 9: Energy Balance, Body Composition, and Weight Management

Energy Balance

Energy balance is governed by a thermodynamic identity: body energy stores change when energy intake differs from energy expenditure. This simple principle is complicated in practice by the fact that both intake and expenditure are highly regulated by biological systems that resist deviation from a defended body weight.

The Harris-Benedict equations, and their more accurate modern successors such as the Mifflin-St Jeor equations, estimate BMR from body weight, height, age, and sex:

where \(W\) is weight in kg, \(H\) is height in cm, and \(A\) is age in years. TEE is estimated by multiplying BMR by a physical activity factor ranging from 1.2 (sedentary) to 1.9 (very active).

Obesity and Weight Management

Obesity is defined clinically by a body mass index (BMI) of 30 kg/m² or greater, though BMI — computed as \( \text{BMI} = W / H^2 \) — is an imperfect proxy for adiposity because it does not distinguish fat mass from lean mass and does not account for fat distribution. Waist circumference and waist-to-hip ratio are complementary indicators that capture abdominal (visceral) adiposity, which is more metabolically deleterious than peripheral subcutaneous fat.

The pathophysiology of obesity involves a complex interplay of genetic predisposition (GWAS studies have identified hundreds of loci associated with BMI), epigenetic programming, neuroendocrine regulation (leptin, ghrelin, GLP-1, insulin), gut microbiome composition, and environmental factors including food availability, food marketing, sleep, stress, and physical activity opportunities. Effective weight management requires an energy deficit sufficient to mobilise body fat while preserving lean mass, best achieved through a combination of modest dietary energy restriction and increased physical activity.

Chapter 10: Sport Nutrition and Supplements

Fuelling Exercise

The macronutrient fuel mixture oxidised during exercise depends on exercise intensity, duration, and training status. At low-to-moderate intensities, fat oxidation predominates, while carbohydrate oxidation increases progressively with intensity and becomes the primary fuel above approximately 70% of maximal oxygen uptake (VO₂max). During very high-intensity exercise, phosphocreatine hydrolysis and anaerobic glycolysis supply ATP faster than mitochondrial oxidative phosphorylation can.

Carbohydrate availability critically limits endurance performance because the body’s glycogen stores (approximately 500 g in liver and muscle combined) can be depleted within 60–90 minutes of continuous moderate-to-high-intensity exercise. Strategic carbohydrate intake before, during, and after exercise — the timing, amount, and composition of which are active areas of research — is the nutritional intervention with the strongest evidence base in sport nutrition.

Protein needs are elevated in athletes not only to support muscle protein synthesis stimulated by resistance training but also to repair exercise-induced muscle damage and to fuel gluconeogenesis during prolonged endurance efforts. Leucine, a branched-chain amino acid, is particularly effective at stimulating muscle protein synthesis via activation of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway.

Dietary Supplements

The supplement industry in Canada is regulated under the Natural Health Products Regulations, which require that products have a Natural Product Number (NPN) and that labelled claims have evidentiary support. Despite this regulatory framework, the quality and efficacy of supplements vary enormously. Among the many hundreds of supplements marketed to athletes and the general public, only a small number have strong evidence for efficacy at meaningful magnitudes: creatine monohydrate (increases phosphocreatine availability, enhancing power output in high-intensity efforts), caffeine (adenosine receptor antagonist, reduces perception of effort and fatigue), beta-alanine (increases muscle carnosine content, buffering hydrogen ions during high-intensity exercise), and sodium bicarbonate (systemic buffer, modest ergogenic effect during supramaximal efforts).

Chapter 11: Nutrition Across the Lifespan

Nutrition and Aging

As adults age beyond the fifth decade, a constellation of physiological changes alters both nutrient requirements and the capacity to meet them. Lean body mass declines progressively (sarcopenia), reducing BMR and daily energy requirements; yet micronutrient requirements may remain stable or increase. This creates a narrowing of the margin between energy intake — which decreases with reduced physical activity, appetite, and sensory enjoyment of food — and the micronutrient density needed to maintain health. Older adults who restrict energy intake to avoid weight gain risk falling short of requirements for calcium, vitamin D, B12, and other nutrients unless food choices are nutrient-dense.

Vitamin B12 absorption deserves particular mention in the context of aging. In older adults, atrophic gastritis — a chronic inflammatory condition affecting the gastric mucosa — reduces the secretion of hydrochloric acid and intrinsic factor. While intrinsic factor is required for the absorption of food-bound B12 in the ileum, the crystalline B12 found in fortified foods and supplements does not require intrinsic factor and is therefore absorbed by passive diffusion even when gastric secretory function is impaired. This is why health authorities recommend that adults over 50 obtain much of their B12 from fortified foods or supplements.

Food Politics and the Social Determinants of Diet

Dietary behaviour is shaped by forces that extend far beyond individual knowledge and motivation. Food politics encompasses the complex relationships between food producers, manufacturers, retailers, governments, and consumers that determine which foods are available, affordable, and culturally normalised. Agricultural subsidies influence the relative prices of commodity foods. Marketing and advertising — disproportionately directed at children — shape food preferences and brand loyalty. Trade policies determine the international flow of food commodities. And the deliberate blurring of the line between nutrition science and marketing — through industry-funded research, strategic philanthropy directed at professional organisations, and the cultivation of academic relationships — has repeatedly distorted nutritional guidance in ways that served commercial interests at the expense of public health.

Food insecurity — the state of uncertain, insufficient, or unacceptable access to food — affects a substantial proportion of Canadians, with disproportionate prevalence among Indigenous communities, racialized groups, single-parent households, and individuals with low incomes. Food-insecure households are more likely to consume energy-dense, nutrient-poor diets, not because of ignorance about healthy eating but because nutritious foods are more expensive per calorie, require time and equipment to prepare, and may not be available in under-resourced communities.