Obesity is among the most important medical problems in America today. Currently, approximately 1 in 4 children and 1 in 2 adults are overweight, prevalence rates that have increased by 50% since the 1960s. In an attempt to combat this problem, the Federal government and various official medical agencies have advocated decreasing intake of total fat and sugar, while increasing consumption of "complex carbohydrate." Despite a recent reduction in fat consumption to near the recommended 30% of total energy, rates of obesity have continued to rise, suggesting that other dietary factors may play a critical role in body weight regulation. One such factor may be glycemic index. This review examines the physiologic effects of glycemic index and argues for the need for controlled clinical trials of a low glycemic index diet in the treatment of obesity. (+info)
Sensory exploitation as an evolutionary origin to nuptial food gifts in insects.
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Nuptial food gifts given by males to females at mating are widespread in insects, but their evolutionary origin remains obscure. Such gifts may arise as a form of sensory trap that exploits the normal gustatory responses of females, favouring the selective retention of sperm of gift-giving males. I tested this hypothesis by offering foreign food gifts, synthesized by males of one cricket species, to females of three non-gift-giving species. Females provisioned with novel food gifts were 'fooled' into accepting more sperm than they otherwise would in the absence of a gift. These results support the hypothesis that nuptial food gifts and post-copulatory female mating preferences coevolve through a unique form of sensory exploitation. (+info)
Experimental tests of predation and food hypotheses for population cycles of voles.
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Pronounced population cycles are characteristic of many herbivorous small mammals in northern latitudes. Although delayed density-dependent effects of predation and food shortage are often proposed as factors driving population cycles, firm evidence for causality is rare because sufficiently replicated, large-scale field experiments are lacking. We conducted two experiments on Microtus voles in four large predator-proof enclosures and four unfenced control areas in western Finland. Predator exclusion induced rapid population growth and increased the peak abundance of voles over 20-fold until the enclosed populations crashed during the second winter due to food shortage. Thereafter, voles introduced to enclosures which had suffered heavy grazing increased to higher densities than voles in previously ungrazed control areas which were exposed to predators. We concluded that predation inhibits an increase in vole populations until predation pressure declines, thus maintaining the low phase of the cycle, but also that population cycles in voles are not primarily driven by plant-herbivore interactions. (+info)
The food-derived carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine activates S-phase checkpoint and apoptosis, and induces gene mutation in human lymphoblastoid TK6 cells.
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The mutagenic heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-blpyridine (PhIP) is formed at parts per billion levels when meat is cooked. It is efficiently absorbed from cooked food and extensively activated to its genotoxic N-hydroxy derivative by human cytochrome P4501A enzymes. It is also a rodent carcinogen. To better understand the genetic toxicity of PhIP, we have examined its effect on the cell cycle and gene mutation frequency using human lymphoblastoid cells (TK6) as a model. Because TK6 cells are unable to activate PhIP, we have cultured the cells in the presence of irradiated Chinese hamster XEMh1A2-MZ cells that have been genetically engineered to express human CYP1A2. Asynchronized TK6 cells were harvested at various times after treatment with PhIP (1.25-10 microg/ml), fixed and stained with propidium iodide for the examination of cell cycle by fluorescence-activated flow cytometry. After 20 h of PhIP treatment, a slight S-phase delay of the cell cycle was observed. Normal cell cycle recovered after the cells were washed and further cultured in the absence of PhIP for 5 days. However, PhIP treatment for 40 h induced a more pronounced S-phase arrest that was accompanied by a decrease in the level of cyclin A, an S-phase cyclin. This was followed by the appearance of a sub-G1 population (indicative of apoptotic cell death), range from 13 to 54% with PhIP concentrations from 1.25 to 10 microg/ml, compared with 5% in the vehicle control. A concomitant increase of mutation frequency at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus, assessed by colony formation assay in the presence of 6-thioguanine, was detected after 40 h-range, 16 to 45 x 10(-6) compared with 12 x 10(-6) in cultures without PhIP. In G1-enriched cell populations (synchronized culture), although PhIP induced S-phase delay, the induction of sub-G1 cells was substantially decreased. Our studies show that in TK6 cells, PhIP activates S-phase checkpoint, yet eludes G1 and G2-M checkpoints, and is accompanied by increased apoptosis and gene mutation. If treatment with PhIP induces similar cellular reactions in vivo, then activation of S-phase checkpoint with avoidance of G1 and G2-M checkpoints could be important factors in PhIP-induced genetic damage and neoplastic disease. (+info)
Postprandial chylomicrons and VLDLs in severe hypertriacylglycerolemia are lowered more effectively than are chylomicron remnants after treatment with n-3 fatty acids.
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BACKGROUND: n-3 Fatty acids lower plasma triacylglycerols not only in the fasting state but also in the postprandial state. However, it is not known whether chylomicrons, chylomicron remnants, and VLDLs are all affected equally or whether some lipoprotein species are lowered preferentially. OBJECTIVE: Lipoproteins, including large and small chylomicron remnants, were determined specifically with the aid of a newly developed method involving a combination of size-exclusion chromatography and fluorometric determination of retinyl palmitate, which served as a marker for exogenous fat. DESIGN: Twelve hypertriacylglycerolemic men were treated for 6 wk with 4 capsules containing 85% fish-oil concentrate/d; each capsule contained 850 mg n-3 fatty acid ethyl esters (49.1% eicosapentaenoic acid by wt and 32.2% docosahexaenoic acid by wt). Oral-fat-tolerance tests were performed before and after the treatment. Blood samples were drawn in the fasting state and until 8 h postprandially. RESULTS: Treatment with n-3 fatty acids reduced the fasting VLDL-triacylglycerol concentration by 44% (P < 0.05) and postprandial chylomicrons and VLDLs at 4, 6, and 8 h (P < 0.05) by 49-64% and 36-43%, respectively. Chylomicron remnants were reduced only in the late postprandial phase: large chylomicron remnants by 19% at 6 h and by 43% at 8 h (P < 0.05) and small chylomicron remnants by 31% at 8 h (P < 0.05). CONCLUSION: n-3 Fatty acids effectively lower chylomicrons and VLDLs, but their effect on chylomicron remnants was observed only in the late postprandial phase. (+info)
Estimation of nonheme-iron bioavailability from meal composition.
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BACKGROUND: Considerable data are available on the individual effects of dietary factors on nonheme-iron absorption, but their combined effect when they are present in the same meal is not known. OBJECTIVE: Our objective was to predict the bioavailability of iron from complex meals that are consumed commonly in the United States on the basis of the contents of factors that are known to promote or inhibit food iron absorption. DESIGN: Radioisotopic measurements of nonheme-iron absorption from 25 meals were made in 86 volunteer subjects by using extrinsic radioiron labeling. The meal contents of nonheme iron, calcium, ascorbic acid, polyphenols, and phytic acid were determined by biochemical analysis; energy and protein contents were estimated from food-composition tables. Animal tissue content was based on weight or was obtained from the manufacturer. RESULTS: After adjusting iron absorption for differences in iron status, the significant biochemical predictors of iron absorption as determined by multiple regression analysis were the contents of animal tissue (P = 0.0001), phytic acid (P = 0.0001), and ascorbic acid (P = 0. 0441). Collectively, these 3 variables accounted for 16.4% of the variation in absorption. On the basis of the multiple regression analysis, we developed the following equation to estimate iron absorption: Ln absorption, % (adjusted to serum ferritin concentration of 30 microg/L) = 1.9786 + (0.0123 x animal tissue in g) - (0.0034 x phytic acid in mg) + (0.0065 x ascorbic acid in mg). CONCLUSION: For the 25 meals evaluated, only the contents of animal tissue, phytic acid, and ascorbic acid were useful for estimating nonheme-iron absorption. (+info)
Activation of macrophages by food antigens: enhancing effect of gluten on nitric oxide and cytokine production.
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Macrophages play an important role in effector mechanisms of various chronic inflammatory diseases. We studied the effect of gluten, the agent inducing celiac disease, and other food antigens on the activation of macrophages. Nitric oxide (NO) and cytokine production were followed as markers of activation, using cultured murine peritoneal macrophages. None of the food antigens tested caused direct inducible nitric oxide synthase (iNOS) activation in macrophages. Unlike other food antigens gluten, gliadin, and their proteolytic fragments significantly enhanced NO production when applied together with interferon-gamma (IFN-gamma), the most efficient being fragments originating from 25- to 45-min peptic digestion. The activation pathway was mediated via direct stimulation of tumor necrosis factor alpha (TNF-alpha) secretion. The NO-enhancing effect was confirmed at the level of iNOS mRNA transcription. In case of sustained local inflammatory reaction connected with increase of IFN-gamma, gluten and its proteolytic fragments may thus elevate NO production. Increased NO level could consequently participate in the development of mucosal lesions in the gut of celiac patients. (+info)
Glutamate and the flavor of foods.
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Investigations of the effects of glutamic acid or its salts on the flavor, hedonic characteristics or acceptance of foods have emphasized a sodium salt of L-glutamic acid, monosodium glutamate (MSG). Food palatability increased with appropriate concentrations of MSG, and could be represented f(MSG and NaCl) as points on the surface of an elliptic paraboloid. Hedonic effects differed between foods, were a function of concentrations of MSG and other ingredients and did not necessarily become positive when only MSG was added. For example, with boiled or fried rice, ratings were neutral or negative with MSG alone, positive for fried rice with MSG and NaCl, but positive for boiled rice only if soy sauce was also added. A one-dish meal, Chinese noodle, became positive with an appropriate concentration of NaCl plus a MSG-5'ribonucleotide mixture, but not with NaCl alone. Flavor of meat, fish or vegetable stocks containing natural glutamates differed from that of quinine, sucrose, NaCl or acid solutions. Glutamates and free amino acids plus nucleotides were necessary for full boiled potato flavor. Overall, the effects of MSG on foods were different from those of NaCl but often interacted with NaCl, and positive effects were facilitated by low concentrations of 5'-ribonucleotides. (+info)