We evaluated the effects of maternal dietary flaxseed during lactation on milk composition, body composition and sexual function of the adult female offspring. The dams were fed a control casein diet (C) or flaxseed diet (F, 25%) throughout lactation. F mothers showed higher serum 17beta-estradiol (E2) and leptin at weaning. F mother's milk had lower total cholesterol (TC) and higher E2 and leptin. The offspring of F dams showed lower body mass (BM), body fat mass (BFM), visceral fat mass (VFM), TC and triglycerides (TG) and higher serum leptin and E2 at 21 days. F offspring showed delayed puberty onset. At 150 days, these offspring presented higher BFM, VFM, TC, TG, E2 and lower relative uterine weight and lower progesterone. In conclusion, flaxseed during lactation did affect the lipid profile, adipose tissue and sexual function in adulthood, probably due hyperestrogenism and hyperleptinemia at weaning.

Maternal intake of flaxseed in the diet during lactation produces early insulin sensitivity and hyperleptinemia; these hormonal imprinting factors could program for selective insulin resistance, since the higher insulin serum concentration was not associated with higher adiposity. These findings, associated with lower serum adiponectin concentration in adulthood, could indicate an increased risk for later development of diabetes mellitus.

We evaluated maternal intake of SDG (secoisolariciresinol diglucoside), a compound from flaxseed, and flaxseed oil+SDG on biochemical and hormonal parameters of dams and male and female offspring during lactation. Dams were fed a standard diet (C); diet added 40 mg of SDG/100g diet (SDG) or diet added 40 mg of SDG/100g diet and 7% of flaxseed oil (OLSDG). SDG and OLSDG dams showed hyperprolactinemia. The OLSDG milk had lower lactose and protein, while the SDG milk had lower protein on the 14th day of lactation. At 14 days, OLSDG male and female pups showed lower body mass, SDG and OLSDG male pups had hypoprolactinemia and lower body fat mass, but higher visceral fat mass (VFM) and hypertriglyceridemia. At 21 days, male SDG and OLSDG presented hypotriglyceridemia. At 14 days, SDG and OLSDG female offspring showed higher serum 17-β estradiol (E2); OLSDG presented hypercholesterolemia and SDG presented hypertriglyceridemia. At 21 days, SDG and OLSDG female pups showed hypotriglyceridemia and OLSDG shower lower E2. Both maternal treatments changes maternal metabolism as well as hormonal and biochemical parameters of the offspring, which are gender-dependent. Maternal hyperprolactinemia may act as an imprint factor responsible for the hormonal and metabolic changes observed in the pups.

Maternal flaxseed supplementation decreases offspring adiposity and increases pituitary leptin signaling at weaning, but it induces hypertrophic adipocytes and higher thyroid leptin receptor in adulthood. The present data suggest that extensive use of flaxseed during lactation is undesirable.

Flaxseed has several benefits for health such as improvement in lipid profile; and since thyroid hormones increases cholesterol biliary excretion, we decide to evaluate the programming effect of maternal flaxseed diet during lactation upon thyroid hormone metabolism and action in the adult offspring in rats. At birth, lactating rats were divided into: flaxseed dams (F) - diet with 25% of flaxseed - and controls dams (C). F and C pups received normal diet after weaning and male offspring were sacrificed at 21 and 180 days old. We evaluated serum T3, T4, and TSH; type 1 and 2 deiodinase activities (D1 and D2) in the liver, thyroid, brown adipose tissue (BAT), and pituitary; thyroid hormone receptor (TRβ1) expression and mitochondrial glycerophosphate-dehydrogenase activity (GPDm) in the liver. F offspring showed lower T3 levels at weaning (-30%, p<0.05) probably caused by lower liver D1 activity (-32%, p<0.05) and higher TSH levels (+84.6%, p<0.05) characterizing a profile of hypothyroidism. At 180 days old, F offspring had lower T4 and thyroid D1 and D2 activities (-28.3%, -18.5%, and -44.2%, respectively, p<0.05) and higher BAT D2 activity (+34.5%, p<0.05). We suggest that adult F animals present an inappropriate TSH action on the thyroid, since thyroid deiodinase was lower. Serum T3 was normal probably due to a higher BAT D2 activity and may reflect the tissue T3 concentration because liver D1, TRβ1, and GPDm were normal. Thus, maternal flaxseed diet during lactation may affect the thyroid hormones metabolism in a long-term.