Nutritional impact of elevated calcium transport activity in carrots

Abstract

Nutrition recommendations worldwide emphasize ingestion of plant-based diets rather than diets that rely primarily on animal products. However, this plant-based diet could limit the intake of essential nutrients such as calcium. Osteoporosis is one of the world's most prevalent nutritional disorders, and inadequate dietary calcium is a known contributor to the pathophysiology of this condition. Previously, we have modified carrots to express increased levels of a plant calcium transporter (sCAX1), and these plants contain approximately 2-fold-higher calcium content in the edible portions of the carrots. However, it was unproven whether this change would increase the total amount of bioavailable calcium. In randomized trials, we labeled these modified carrots with isotopic calcium and fed them to mice and humans to assess calcium bioavailability. In mice feeding regimes (n = 120), we measured (45)Ca incorporation into bones and determined that mice required twice the serving size of control carrots to obtain the calcium found in sCAX1 carrots. We used a dual-stable isotope method with (42)Ca-labeled carrots and i.v. (46)Ca to determine the absorption of calcium from these carrots in humans. In a cross-over study of 15 male and 15 female adults, we found that when people were fed sCAX1 and control carrots, total calcium absorption per 100 g of carrots was 41% +/- 2% higher in sCAX1 carrots. Both the mice and human feeding studies demonstrate increased calcium absorption from sCAX1-expressing carrots compared with controls. These results demonstrate an alternative means of fortifying vegetables with bioavailable calcium.

Fig. 1.

Percentage of incorporation of ⁴⁵Ca into female and male mice bones after a single meal from extrinsically and intrinsically labeled carrot diets. (A) Thirty mice were fed extrinsically labeled control and sCAX1–1 diets, and 10 mice were fed sCAX1–2 carrots. (B) Thirty mice were fed intrinsically labeled control and sCAX1–1-expressing carrot-containing diets.

Fig. 2.

Calcium absorption in female and male human subjects fed single meals containing labeled carrots. (A) Fractional absorption of ⁴²Ca from control and sCAX1-expressing carrots. *, P < 0.001. (B) Total calcium absorbed from 100 g of fresh control and sCAX1-expressing carrots. *, P < 0.001.