Impact of Buttermilk on Cholesterol Concentration and Homeostasis

Overview

The role of low-density lipoprotein cholesterol (LDL-C) in the pathogenesis of cardiovascular disease (CVD) and the clinical benefit of lowering LDL-C in high-risk patients have both been well established. The key contribution of the intestine to whole body cholesterol homeostasis and thus to regulating plasma cholesterol concentrations has also been recognized over the last years. It is now clear that cholesterol homeostasis and hence plasma LDL-C concentrations are maintained by a fine-tuned balance between intestinal cholesterol absorption and endogenous cholesterol synthesis. Cholesterol is a highly hydrophobic molecule and for that reason, its absorption is almost entirely dependent on its solubilizing capacity in bile acid micelles within the intestine. Recent in vitro studies from our laboratory have shown that buttermilk, a unique by-product of butter manufacturing resulting from the churning of cream, has a strong inhibitory effect on cholesterol micelle solubility. This phenomenon is likely due to the presence of unique milk fat globule membrane (MFGM) fragments present in buttermilk that are produced during the manufacturing of dairy cream into butter. Most of the work done so far on the subject has focused on phospholipids purified from MFGM, while overlooking the complex and entire MFGM mixture of bioactive proteins and polar lipids found in buttermilk. To the best of our knowledge, no study has yet documented the impact of whole buttermilk on plasma cholesterol concentration in human. The general objective of this research project is to investigate for the first time the impact of buttermilk on plasma cholesterol and other risk factors for CVD in humans. More specifically, we propose to investigate the impact of buttermilk consumption on plasma LDL-C and other CVD risk factors as well as on plasma surrogates of cholesterol absorption and synthesis.

The proposed research will be undertaken as a double-blind randomized cross-over study with participants being subjected to 2 consecutive treatments of 4 weeks each, in random order, during which they will consume 45g of buttermilk and a macro- and micronutrient matching placebo. The treatments will be different in their content of MFGM (present in buttermilk, absent in placebo). Buttermilk and placebo will be fully characterized and formulated in ready-to-use pouches, each pouch containing 22.5 g of artificially flavored products that will have to be mixed in a fixed amount of water for consumption. Participants will have to consume two pouches every day. Based on a 2500 kcal/day regimen, we have calculated that these placebo and buttermilk formulation will contribute to approximately 200 kcal (from 5% and 10%) of the daily energy intake of participants, who will be asked to maintain other aspects of their nutritional habits constant throughout the study. Fluctuations in female hormones have been shown to influence metabolic variables. For that reason, outcomes at the end of each dietary phase will be measured during the follicular phase of menstrual cycle (day 3 to day 9) in pre-menopausal women. This is another argument for using a 4-wk intervention, which essentially corresponds to the mean duration of the menstrual cycle of most women. Pre-menopausal women will start the first diet during the first week of their menstrual cycle.