| Number of essential vitamins | 13 (4 fat-soluble, 9 water-soluble) (National Institutes of Health, Office of Dietary Supplements) |
| Calories per gram: carbohydrates | 4 kcal/g (USDA Dietary Reference Intakes) |
| Calories per gram: protein | 4 kcal/g (USDA Dietary Reference Intakes) |
| Calories per gram: fat | 9 kcal/g (USDA Dietary Reference Intakes) |
| GI threshold for 'low' classification | 55 or below (Glycemic Index Foundation) |
| Daily fibre recommendation (adults) | 22–34 g depending on age and sex (Dietary Guidelines for Americans, 2020–2025) |
Why Nutrition Language Matters
Walk down any grocery aisle or scan a health headline and you'll encounter a steady stream of nutrition terminology — antioxidants, probiotics, net carbs, bioavailability. Without a working vocabulary, these words can feel more like marketing noise than useful information.
This glossary cuts through that noise. The definitions below are drawn from established nutritional science and are written for everyday readers, not clinicians. Understanding these terms won't replace personalized guidance from a registered dietitian, but it will help you ask better questions and read food information more critically.
For a deeper look at how carbohydrates, proteins, and fats function in the body, see our plain-language macronutrient guide. And if you want to put this vocabulary to immediate use, our article on reading a nutrition label is a natural next step.
| Number of essential vitamins | 13 (4 fat-soluble, 9 water-soluble) (National Institutes of Health, Office of Dietary Supplements) |
| Calories per gram: carbohydrates | 4 kcal/g (USDA Dietary Reference Intakes) |
| Calories per gram: protein | 4 kcal/g (USDA Dietary Reference Intakes) |
| Calories per gram: fat | 9 kcal/g (USDA Dietary Reference Intakes) |
| GI threshold for 'low' classification | 55 or below (Glycemic Index Foundation) |
| Daily fibre recommendation (adults) | 22–34 g depending on age and sex (Dietary Guidelines for Americans, 2020–2025) |
Core Nutrition Terms Defined
The terms below cover the concepts that come up most frequently in nutrition discussions — from food science basics to concepts you'll encounter on labels and in health reporting.
Macronutrients
The three main nutrient categories — carbohydrates, proteins, and fats — that provide the body with energy (calories). They are needed in relatively large amounts compared to micronutrients.
Micronutrients
Vitamins and minerals required by the body in small but essential amounts. They don't provide calories but are critical for processes like immune function, bone health, and energy metabolism.
Glycaemic Index (GI)
A scale from 0–100 that ranks how quickly a carbohydrate-containing food raises blood glucose levels compared to pure glucose. High-GI foods cause a faster, more pronounced rise; low-GI foods produce a slower, more gradual response. GI can change depending on cooking method, ripeness, and what else you eat at the same meal.
Bioavailability
The proportion of a nutrient that the body actually absorbs and uses after digestion. A food can be high in a nutrient on paper but deliver far less if bioavailability is low — as is the case with iron from plant sources compared to animal sources.
Dietary Fibre
A type of carbohydrate found in plant foods that the body cannot fully digest. Soluble fibre (found in oats and legumes) dissolves in water and can help moderate blood cholesterol and glucose. Insoluble fibre (found in whole grains and vegetables) adds bulk to stool and supports regular digestion.
Antioxidants
Compounds — including vitamins C and E, selenium, and various plant pigments — that help neutralise unstable molecules called free radicals. Free radical accumulation is linked to cell damage; a diet rich in fruits and vegetables provides a broad range of antioxidants.
Probiotics
Live microorganisms that, when consumed in adequate amounts, may confer a health benefit on the host, primarily through supporting gut microbiome balance. Common sources include fermented foods like yogurt, kefir, and kimchi.
Prebiotics
Non-digestible food components — mainly certain fibres — that selectively feed beneficial bacteria in the gut. Garlic, onions, bananas, and oats are naturally rich prebiotic sources.
Empty Calories
Calories from foods that provide energy (from sugar or fat) but little to no accompanying vitamins, minerals, or fibre. Sugary beverages and heavily processed snack foods are common examples.
Nutrient Density
A measure of how many beneficial nutrients a food provides relative to its calorie content. Leafy greens, for instance, are highly nutrient-dense — rich in vitamins and minerals for very few calories.
Phytonutrients
Natural compounds produced by plants — including flavonoids, carotenoids, and polyphenols — that may support health beyond basic nutrition. Research into their effects is ongoing; they are not classified as essential nutrients but are associated with diets linked to positive health outcomes.
Saturated vs. Unsaturated Fat
Saturated fats are solid at room temperature (found in butter and red meat) and are associated with raising LDL cholesterol when consumed in excess. Unsaturated fats — monounsaturated and polyunsaturated — are liquid at room temperature (found in olive oil and fatty fish) and are generally considered more favorable for cardiovascular health.
A few of these terms — particularly micronutrients and dietary fibre — deserve more attention than they typically receive. Our companion article on fibre, vitamins, and minerals explores why these nutrients are chronically underestimated and where to find them in everyday foods.
Emerging Research vs. Established Science
Some terms in this glossary — particularly around phytonutrients, the gut microbiome, and antioxidants — reflect areas of active research where the full picture is still being established. When a finding is described as 'associated with' a health outcome rather than proven to cause it, that distinction is intentional and important. Promising research in nutrition takes years to translate into clinical guidance, and individual responses to foods vary considerably. Always treat emerging findings as context, not prescription.
Putting the Vocabulary to Work
Knowing these terms changes how you engage with nutrition information — on product packaging, in media coverage, and in conversations with healthcare providers.
95%
Americans not meeting fibre recommendations
Research published in the American Journal of Lifestyle Medicine estimates that the vast majority of US adults fall short of recommended daily fibre intake.
~10x
Difference in iron bioavailability: heme vs. non-heme
Heme iron from animal sources is absorbed at roughly 15–35%, while non-heme iron from plants is absorbed at approximately 2–20%, depending on dietary context.
39 million+
Americans with inadequate vitamin D levels
According to National Health and Nutrition Examination Survey data, a significant share of US adults have vitamin D insufficiency — illustrating why bioavailability and dietary source matter.
For example, understanding bioavailability helps explain why spinach is a less efficient source of iron than red meat, and why pairing plant-based iron with vitamin C can close that gap. Knowing the difference between soluble and insoluble fibre helps you choose foods that support both gut health and satiety. And recognising that the glycaemic index of a food shifts when you combine it with fats or proteins prevents oversimplified conclusions about carbohydrates.
Nutrition labels are one of the most practical places to apply this vocabulary. Many of the terms on labels are misunderstood even by attentive shoppers — our article on nutrition label myths walks through the most common points of confusion.
Movement and nutrition are closely linked, too. If you're exploring how food choices support physical activity, the Fitness & Movement hub offers approachable strategies for everyday Americans.
This article is for general informational and educational purposes only and does not constitute medical or nutritional advice. For guidance tailored to your individual health needs, consult a registered dietitian or qualified healthcare professional.
NIH Office of Dietary Supplements: Nutrient Fact Sheets
The National Institutes of Health publishes detailed, evidence-based fact sheets on individual vitamins and minerals — an authoritative reference for anyone wanting to go deeper than a glossary.
USDA FoodData Central
A free, searchable database that shows the nutrient composition of thousands of foods — useful for seeing how macros, fibre, and micronutrients stack up in what you actually eat.
Dietary Guidelines for Americans
The federal government's evidence-based framework for healthy eating patterns, updated every five years. A reliable reference for understanding recommended intakes and food group guidance.