Fad Diet Ingredients Decoded: A Reference Glossary

MCT Oil

Medium-chain triglycerides (MCTs) are a type of saturated fat found naturally in coconut oil and palm kernel oil. Because of their shorter molecular chain, they are absorbed more quickly than most dietary fats and converted into energy more readily. MCT oil is popular in ketogenic and low-carb diet products.

Resistant Starch

A type of starch that resists digestion in the small intestine and instead ferments in the large intestine, feeding beneficial gut bacteria. It functions similarly to dietary fiber. Common sources include green bananas, cooked-and-cooled potatoes, and certain legumes.

Inulin

A naturally occurring prebiotic fiber found in foods like chicory root, garlic, onions, and artichokes. It feeds beneficial gut bacteria and can help improve bowel regularity. It is often added to processed foods as a fiber supplement or fat replacer.

Adaptogens

A loose category of plant-based substances — including ashwagandha, rhodiola, and holy basil — traditionally used in herbal medicine with the claimed ability to help the body manage stress. Research on individual adaptogens varies considerably in quality and scope.

Collagen Peptides

Short chains of amino acids derived from animal connective tissue, sold as a protein supplement. The body does not absorb collagen intact; it breaks it into amino acids like any other protein. Evidence for specific benefits such as skin or joint improvements is mixed.

Psyllium Husk

A soluble fiber derived from the seeds of the Plantago ovata plant. It absorbs water in the digestive tract, forming a gel that slows digestion and can support regular bowel movements. It is one of the better-studied dietary fiber supplements.

Exogenous Ketones

Ketone bodies — most commonly beta-hydroxybutyrate (BHB) — supplied directly through a supplement rather than produced by the body through fasting or a ketogenic diet. They raise blood ketone levels temporarily, though whether this mirrors the metabolic effects of nutritional ketosis is debated.

Ashwagandha

An herb used in Ayurvedic medicine, classified as an adaptogen. Some clinical studies suggest it may help reduce self-reported stress and cortisol levels in certain populations, though study sizes are often small. It is widely added to stress-support and wellness products.

Apple Cider Vinegar (ACV)

A fermented liquid made from crushed apples, containing acetic acid and trace amounts of vitamins and minerals. It is frequently marketed for blood sugar management and weight loss. The evidence base is limited, with most studies being small or short-term.

Prebiotics vs. Probiotics

Prebiotics are non-digestible fibers (like inulin) that feed beneficial gut bacteria. Probiotics are live bacteria or yeasts added to foods or supplements to directly contribute to gut microbiome populations. Both are often found in diet and wellness products, sometimes together.