Milk

Milk is a specialized mammalian secretion that Ray Peat considered the optimal food for supporting high metabolic rate and brain development, largely because it provides rapidly absorbable nutrients without the defensive chemicals found in plant foods. 2 The rumen of a cow converts cellulose, lignin, and protein into a mixture of sugar, highly saturated fat, and peptides, which the animal then digests. 1 For the human consuming it, milk supplies lactose, which is quickly metabolized into glucose, along with small amounts of progesterone and thyroid hormone that favor efficient energy use. 2 This hormonal and energetic support explains why brain growth is extremely rapid during the nursing period, continuing the trajectory of intrauterine development. 2 Peat argued that nervous systems process substance meaningfully, not just information, and that milk provides the substance for a developing brain to express its integral vitality. 2

A central mechanism of milk's benefit is its high calcium content and its ability to suppress parathyroid hormone (PTH). 2 Peat explained that a dietary calcium deficiency causes PTH to rise, which leads to bone softening, soft tissue calcification, high blood pressure, and increased inflammation. 2 He cited evidence that higher dietary calcium is independently associated with a lower risk of kidney stones, directly contradicting the common medical warning. 2 The calcium in milk is uniquely well-absorbed because its proteins prepare the intestinal lining for efficient uptake of both calcium and magnesium. 4 Peat noted that consuming a large portion of the day's calcium at bedtime can reduce the nocturnal rise of PTH and the resulting loss of calcium from bones. 2 This PTH-suppressing effect is also the basis for milk's role as a weight-loss food; Peat pointed to studies showing that increased calcium and vitamin D reduce obesity by stimulating calorie-burning uncoupling proteins and inhibiting fat-producing enzymes. 2

Peat addressed common objections to milk consumption by contextualizing its components. The hormones in milk, including testosterone and progesterone, are present in amounts that are protective for the young animal, and human breast milk contains enough thyroid to prevent hypothyroid symptoms in infants with damaged thyroids. 3 While milk does contain minuscule amounts of estrogen, Danny Roddy has written that this estrogen comes "prepackaged" with enzymes that make it readily available for excretion upon ingestion. 5 Regarding the growth factor IGF-1, Peat argued that its stimulation by milk is not inherently harmful, as it is just one of many overlapping regulatory systems, and its effects are species-specific. 2 He also noted that the natural trans-fats in dairy are precursors to conjugated linoleic acid, a component with anti-inflammatory and anti-obesity effects that can block harmful polyunsaturated fats. 8

For adults, Peat recognized that milk's biological purpose as a growth medium means its methionine and tryptophan content is higher than optimal, and its phosphate ratio is slightly elevated relative to calcium. 10 However, he considered its low iron content a significant advantage for preventing the iron overload that contributes to degenerative diseases. 10 The fat content should be adjusted to activity level; Peat personally switched to 1% milk when he noticed weight gain from whole milk during a sedentary period in graduate school. 4 For those who cannot tolerate milk, he recommended cooked greens as an alternative calcium source due to their high calcium-to-phosphate ratio, though he maintained that nothing is as effective as milk for optimizing calcium and magnesium absorption. 2 Roddy has extended this by outlining strategies for overcoming lactose intolerance, including introducing small amounts with meals, suppressing bacterial endotoxin with a raw carrot, and consuming milk with plenty of sugar and salt to restrain adaptive stress hormones. 5