Major scientific advances with dairy foods in nutrition and health.

A large body of scientific evidence collected in recent decades demonstrates that an adequate intake of calcium and other nutrients from dairy foods reduces the risk of osteoporosis by increasing bone acquisition during growth, slowing age-related bone loss, and reducing osteoporotic fractures. These results have culminated in the new (2005) Dietary Guidelines for Americans that now recommend 3 servings of milk products per day to reduce the risk of low bone mass and contribute important amounts of many nutrients that may have additional health attributes beyond bone health. A number of animal, observational, and clinical studies have shown that dairy food consumption can help reduce the risk of hypertension. Clinical trials indicate that the consumption of recommended levels of dairy products, as part of a healthy diet, can contribute to lower blood pressure in individuals with normal and elevated blood pressure. Emerging data also indicate that specific peptides associated with casein and whey proteins can significantly lower blood pressure. In addition, a growing body of evidence has provided support for a beneficial effect of dairy foods on body weight and fat loss. Clinical studies have demonstrated that during caloric restriction, body weight and body fat loss occurs when adequate calcium is provided by supplements and that this effect is further augmented by an equivalent amount of calcium supplied from dairy foods. Several studies support a role for calcium, vitamin D, and dairy foods against colon cancer. Additionally, conjugated linoleic acid, a fatty acid found naturally in dairy fat, confers a wide range of anticarcinogenic benefits in experimental animal models and is especially consistent for protection against breast cancer.

Effects of dietary calcium on adipocyte lipid metabolism and body weight regulation in energy-restricted aP2-agouti transgenic mice.

We have demonstrated previously a regulatory role for intracellular Ca2+ ([Ca2+]i) in adipocyte lipogenesis and lipolysis and have recently reported that 1,25-(OH)2-D increases adipocyte [Ca2+]i, which causes increased lipogenesis and decreased lipolysis. We have now tested the hypothesis that suppressing 1,25-(OH)2-D by increasing dietary calcium will suppress adipocyte [Ca2+]i, thereby facilitating weight loss by stimulating lipolysis and inhibiting lipogenesis in calorically (Kcal)-restricted (70% of ad lib) aP2-agouti transgenic (aP2-a) mice. Mice (aP2-a) exhibiting a pattern of obesity gene expression similar to humans were fed a low-Ca (0.4%)/high-fat/high-sucrose diet for six weeks, resulting in a 27% and twofold increase in body weight and total fat pad mass, respectively, with a twofold increase in adipocyte [Ca2+]i pad lib or Kcal-restricted (70% of ad lib) on this diet either unsupplemented (basal) or with 25% or 50% of the protein replaced by non-fat dry milk (medium or high) dairy or supplemented with CaCO3 to 1.2% Ca for six weeks. Adipocyte [Ca2+]i was unaffected by Kcal restriction but was reduced markedly by all three high Ca diets (290 vs. 130 nM, p2+]i and thereby reduce energy storage and increase thermogenesis during Kcal restriction.

Regulation of adiposity by dietary calcium.

Recent data from this laboratory demonstrate that increasing adipocyte intracellular Ca(2+) results in a coordinated stimulation of lipogenesis and inhibition of lipolysis. We have also noted that increasing dietary calcium of obese patients for 1 year resulted in a 4.9 kg loss of body fat (P<0.01). Accordingly, we tested the possibility that calcitrophic hormones may act on adipocytes to increase Ca(2+) and lipid metabolism by measuring the effects of 1, 25-(OH)(2)-D in primary cultures of human adipocytes, and found significant, sustained increases in intracellular Ca(2+) and a corresponding marked inhibition of lipolysis (EC(50) approximately 50 pM; P<0.001), suggesting that dietary calcium could reduce adipocyte mass by suppressing 1,25-(OH)(2)-D. To test this hypothesis, we placed transgenic mice expressing the agouti gene specifically in adipocytes on a low (0.4%) Ca/high fat/high sucrose diet either unsupplemented or with 25 or 50% of the protein replaced by non-fat dry milk or supplemented to 1.2% Ca with CaCO(3) for 6 wk. Weight gain and fat pad mass were reduced by 26-39% by the three high calcium diets (P<0.001). The high calcium diets exerted a corresponding 51% inhibition of adipocyte fatty acid synthase expression and activity (P<0.002) and stimulation of lipolysis by 3. 4- to 5.2-fold (P<0.015). This concept of calcium modulation of adiposity was further evaluated epidemiologically in the NHANES III data set. After controlling for energy intake, relative risk of being in the highest quartile of body fat was set to 1.00 for the lowest quartile of Ca intake and was reduced to 0.75, 0.40, and 0.16 for the second, third, and fourth quartiles, respectively, of calcium intake for women (n=380;P<0.0009); a similar inverse relationship was also noted in men (n=7114; P<0.0006). Thus, increasing dietary calcium suppresses adipocyte intracellular Ca(2+) and thereby modulates energy metabolism and attenuates obesity risk.

Benefits of dairy product consumption on blood pressure in humans: a summary of the biomedical literature.

The inverse relationship between intake of dairy products and blood pressure levels was first suggested by several epidemiologic surveys in the early 1980's that revealed low calcium intake in populations with increased prevalence of hypertension. Subsequent laboratory and clinical investigations provided further evidence of the association between calcium and blood pressure, but the results of these studies were often inconsistent due to variations in study design and methods, study participants and calcium sources. The recently published results of the large and carefully executed Dietary Approaches to Stop Hypertension Study, "DASH," which demonstrated a dramatic blood-pressure lowering effect of diets rich in dairy products, fruits and vegetables, addressed many of the issues contributing to the inconsistencies in the blood pressure-calcium data. In the following review, we discuss the evolution of the scientific evidence of the association between dietary calcium intake and blood pressure, the findings and significance of the DASH trial and the consensus that now exists among health professionals regarding the importance of adequate dairy product intake for optimal blood pressure regulation.

Age considerations in nutrient needs for bone health.

Age exerts a major influence on the nutritional needs for bone health. Age influences the nutrient requirements for bone health by influencing: the growth and development of bone; the deposition of minerals leading to peak bone mass; the rate of bone loss; the levels of hormones which influence bone; the absorption and retention of nutrients required for optimal bone health, physical activity, food intake, and the level of sun exposure. Adequate calcium intake benefits bones at any age. However, dietary calcium needs vary at different ages. In June 1994, a National Institutes of Health expert panel recommended higher calcium intakes than current Recommended Dietary Allowance for several age groups. Many population groups in the United States, including young girls and women, continue to consume significantly less calcium than current recommended levels. In addition, diets low in calcium are often low in many other essential nutrients important for good bone health, including vitamin D, vitamin B6, and magnesium. Dietary recommendations for bone health should be placed in the full context of the total diet rather than a singular emphasis on calcium. To truly benefit consumers, dietary recommendations for bone health should emphasize consumption of foods high in calcium as part of a healthy diet and a healthy lifestyle.

Impact of enteral feeding of a glutamine-supplemented formula on the hypoaminoacidemic response in trauma patients.

Plasma amino acid concentrations were measured during fasting and after 3 days of enteral feeding in 16 trauma patients on a glutamine-supplemented diet and 14 patients on an isonitrogenous control diet. During fasting, total amino acids, including glutamine, were depressed by 50% and this was attributed to a reduction in both essential and nonessential amino acids. The essential amino acid concentrations increased in both groups after feeding. The nonessential amino acid concentrations also increased in the control group but not in the glutamine group during feeding. Repletion of the glutamine extracellular pool was not evident after an average intake of 27.1 g per day of glutamine for 3 days. Nitrogen balance was similar for the two groups during feeding. We conclude that in this study, enteral glutamine did not increase the glutamine plasma concentration. In addition, both formulas improved the hypoaminoacidemia of essential amino acids but only the control diet improved the nonessential amino acids plasma concentration.

Glutamine supplementation of enteral nutrition: impact on whole body protein kinetics and glucose metabolism in critically ill patients.

BACKGROUND: Glutamine-supplemented parenteral nutrition has been reported to attenuate the early postoperative reduction in intracellular glutamine and improve protein synthesis and nitrogen balance. We investigated the effect of an enteral formula or protein and glucose kinetics and nitrogen balance in trauma patients. METHODS: The enteral formula (AlitraQ) provided a mean intake of 0.35 g of glutamine/kg body weight per day to 16 trauma patients and was compared with an isonitrogenous formula that provided a mean of 0.05 g of glutamine/kg body weight per day in 14 trauma patients. After 3 days of feeding, protein kinetics were measured using a 4-hour prime-continuous infusion of L-[1-13C]leucine. Glucose kinetics were measured during the same time interval using prime-continuous infusion of [U-14C]- and [6-3H]glucose. RESULTS: Nitrogen balance was not significantly different in the two groups. There were no significant differences in protein turnover, synthesis, and breakdown between the two groups. There were no significant differences in glucose turnover, oxidation, recycling, and percent of VCO2 from glucose oxidation between the two groups. CONCLUSIONS: Glutamine-enriched enteral formulas are well tolerated by the severely injured patient but provide no additional nutritional advantage compared with standard enteral formulas during the first 3 days of feeding immediately after trauma.

Recent developments in gastrointestinal absorption and tissue utilization of peptides: a review.

Considerable evidence has been accumulated regarding the absorption of dipeptides and tripeptides, yet, even with the growing body of knowledge, the nutritional and metabolic significance of peptide absorption is not fully understood, especially in ruminants. Muscle, mammary gland, liver, kidney, intestinal mucosa, and other tissues either have been shown to have, or are suspected to have, the ability to utilize peptides as a source of AA to meet cellular demands. Investigations suggest that ruminal microbes have the ability to produce substantial amounts of small peptides as a consequence of their hydrolysis of dietary proteins. The extent to which intact peptides may be absorbed into the blood is controversial. Some of the inconsistency in reported observations may be because of limitations of analytical procedures, species differences, or both. Peptide absorption appears to be an important physiological process in ruminants and may constitute the primary source of absorbed AA. The recent observation that the stomach region of the gastrointestinal tract may be an important site of peptide absorption is highly significant. Emerging evidence for the contribution that peptide absorption makes to AA provisioning of ruminants may change some of the currently held views about protein utilization in these unique animals.

Peptide absorption: a review of current concepts and future perspectives.

Absorption of di- and tripeptides from the gastrointestinal tract is accepted as being an important biological phenomenon. The extent to which peptides are absorbed and the nutritional and metabolic significance of peptide absorption remain unclear. Evidence is strong for the existence of multiple peptide transport systems, including one type that is electrogenic in nature and that requires a protonmotive force and cotransports two H+ for every peptide transported. The rate of absorption of peptides can be responsive to level of dietary intake and level of dietary protein. Peptide absorption seems to be an important physiological process in ruminants, and this process may account for a large portion of absorbed amino acids. An important new observation is that the nonmesenteric portion of the portal-drained viscera of the ruminant is a major site of peptide absorption. These new observations may result in a reshaping of the currently accepted theory concerning protein utilization by ruminants.