Hormones, growth factors and peptides in food: what the body does with them

Food-hormone questions involve the substance, its role inside an animal and what happens after it is eaten. Those are separate stages of an explanation. A hormone made within a body is already part of its signaling system; a protein in food encounters digestion. This page follows agency explanations and research reviews across those stages, keeping the studies' methods and limits alongside their findings.

this is general information, not medical advice.

What hormones are

MedlinePlus describes hormones as chemical messengers made by endocrine glands and carried through the bloodstream to tissues and organs. Its account places them in processes including growth, metabolism and reproduction. The term describes a signaling role, rather than a single chemical structure. It does not say how every hormone behaves when present in food.

Wikipedia's peptide-hormone article distinguishes amino-acid-based hormones, including peptides and proteins, from steroid hormones. It describes different interactions with cell membranes and receptors for those classes. The encyclopedia's article on peptides defines peptides as amino-acid chains joined by peptide bonds. A peptide's structure and its role as a messenger are therefore related descriptions, not interchangeable definitions.

Growth hormone and IGF-1 in mammals

Wikipedia's growth-hormone article describes growth hormone, also called somatotropin, as a peptide hormone made in the pituitary gland that stimulates IGF-1 production. Its IGF-1 article describes a protein produced primarily in the liver in response to growth hormone. The GH–IGF-1 axis is the relationship between these signals within mammals.

A 2024 review in Frontiers in Endocrinology explains that growth hormone regulates IGF-I generation and that insulin reaching the liver also influences the liver's response to growth hormone. This concerns the body's own regulation. An invited review of somatotropin and lactation biology describes somatotropin's direct metabolic effects in cattle and indirect effects through the IGF system in milk production, with responses influenced by nutrition and management.

What happens to proteins and peptides in food

The NIDDK explanation of digestion describes food mixing with stomach acid and digestive enzymes, followed by further breakdown and nutrient absorption in the small intestine. It explains that proteins break into amino acids. Digestion and absorption are distinct steps: breaking a molecule apart is different from moving material across the intestinal lining.

Wikipedia's digestion article describes acid creating the environment for pepsin in the stomach. Its pepsin article explains how that enzyme cuts proteins into smaller peptides and amino acids. The small-intestine article describes continued protein breakdown by pancreatic and intestinal enzymes. These accounts describe a sequence of changes to food proteins, rather than assuming they remain intact.

The encyclopedia's PepT1 article describes a transporter at the intestinal lining that moves di- and tripeptides into absorptive cells. These are small peptide fragments. Transport into a lining cell is itself a different step from an intact molecule entering the wider circulation. A statement about small-peptide uptake cannot automatically be extended to an entire protein hormone.

The research literature includes Intestinal absorption of peptides, a 1975 paper in Physiological Reviews. A 2014 review in Nutrition Research Reviews reports substantial uptake of di- and tripeptides, but little unequivocal evidence that larger dietary bioactive peptides cross the healthy adult gut intact into the hepatic portal system at physiologically relevant concentrations. That stated limit is about intact passage and relevant concentrations, rather than whether protein digestion occurs.

A 2018 review in Nutrients describes research into food-derived bioactive peptides. Its abstract identifies digestive breakdown, variable absorption, incomplete understanding of mechanisms and a lack of well-designed clinical trials as barriers to substantial evidence for potential health claims. The research label bioactive does not replace evidence about what reaches which tissue or about an effect in humans.

Wikipedia's bioavailability article discusses absorption and availability for use or storage in nutritional science, noting that physiological state and nutritional status affect the concept. A measured concentration in a food and the proportion available inside a person are different quantities. This distinction helps explain why digestive stability, intestinal transport and study design appear together in peptide research.

These reviews ask where a molecule is measured, not only whether it has a biological name. Material in the digestive tract, material inside intestinal lining cells and material in the portal circulation are different study endpoints. The intact-peptide review focuses on the last of those steps for larger molecules. Its uncertainty statement does not erase its account of small-peptide transport. Conversely, the small-peptide finding does not settle whether a larger food-derived sequence remains intact in a relevant amount.

The dairy question

The FDA's bovine-somatotropin page reports that bST is broken down by digestive enzymes and not absorbed intact, and describes that finding as part of its human-food-safety conclusion. A 1990 evaluation in Science by FDA scientists also considers IGF-I in milk. It reports increased milk IGF-I in the dairy studies it evaluated and concludes, from oral animal studies and absorption estimates, that biologically significant intact IGF-I levels would not be absorbed.

A 1990 animal study in the Journal of Nutrition fed milk from bST-treated and untreated cows to male rats whose pituitary glands had been removed. It reported no difference in the effects of those milks after oral ingestion and no effect on the measured growth indices from milk with added bST. The animal model and measured endpoints define what that experiment directly examined.

The 2008 retail-milk survey in the Journal of the American Dietetic Association compared conventional, rbST-free and organic labels for composition. Its authors reported no meaningful differences across the variables measured. A retail composition survey does not directly measure human absorption or long-term outcomes. Wikipedia's bovine-somatotropin article describes Canada and the European Union taking different regulatory decisions on animal-health and welfare grounds.

A 2017 systematic review recorded in PubMed examined milk intake, circulating IGFs and prostate cancer associations across experimental and observational studies. It reported moderate evidence for increased circulating IGF-I and IGFBP-3 with milk intake, and identified IGF-I as a potential mechanism for observed associations. Its abstract also reports little consistency among animal studies and contradictory findings about IGFBP-3 suppression and tumor progression. Those qualifications belong with its findings.

Steroid hormones in beef: a different chemistry

The FDA's beef-hormone explanation concerns steroids such as estradiol, progesterone and testosterone, rather than the dietary protein discussed above. Its review addresses residues in edible tissue. A 2001 review in APMIS Supplementum describes contrasting U.S. and European rules. Protein-digestion findings therefore do not stand in for a steroid-residue assessment.

The rbST dairy page covers approval and milk-label disputes; the beef-hormone page covers the steroid rules. The organic-standard page explains production-label requirements, another distinct part of food policy.