N-Nitroso compounds in the diet.

N-Nitroso compounds were known almost 40 years ago to be present in food treated with sodium nitrite, which made fish meal hepatotoxic to animals through formation of nitrosodimethylamine (NDMA). Since that time, N-nitroso compounds have been shown in animal experiments to be the most broadly acting and the most potent group of carcinogens. The key role of nitrite and nitrogen oxides in forming N-nitroso compounds by interaction with secondary and tertiary amino compounds has led to the examination worldwide of foods for the presence of N-nitroso compounds, which have been found almost exclusively in those foods containing nitrite or which have become exposed to nitrogen oxides. Among these are cured meats, especially bacon-and especially when cooked; concentrations of 100 micrograms kg(-1) have been found or, more usually, near 10 micrograms kg(-1). This would correspond to consumption of 1 microgram of NDMA in a 100-g portion. Much higher concentrations of NDMA (but lower ones of other nitrosamines) have been found in Japanese smoked and cured fish (more than 100 micrograms kg(-1)). Beer is one source of NDMA, in which as much as 70 micrograms l(-1) has been reported in some types of German beer, although usual levels are much lower (10 or 5 micrograms l(-1)); this could mean a considerable intake for a heavy beer drinker of several liters per day. Levels of nitrosamines have been declining during the past three decades, concurrent with a lowering of the nitrite used in food and greater control of exposure of malt to nitrogen oxides in beer making. There have been declines of N-nitroso compound concentrations in many foods during the past two decades. The small amounts of nitrosamines in food are nonetheless significant because of the possibility-even likelihood-that humans are more sensitive to these carcinogens than are laboratory rodents. Although it is probable that alkylnitrosamides (which induce brain tumors in rodents) are present in cured meats and other potentially nitrosated products in spite of much searching, there has been only limited indirect evidence of their presence.     

Polycyclic aromatic hydrocarbons in the diet.

Polycyclic aromatic hydrocarbons (PAHs), of which benzo[a]pyrene is the most commonly studied and measured, are formed by the incomplete combustion of organic matter. They are widely distributed in the environment and human exposure to them is unavoidable. A number of them, such as benzo[a]pyrene, are carcinogenic and mutagenic, and they are widely believed to make a substantial contribution to the overall burden of cancer in humans. Their presence in the environment is reflected in their presence at detectable levels in many types of uncooked food. In addition, cooking processes can generate PAHs in food. PAHs can also be formed during the curing and processing of raw food prior to cooking. Several studies have been carried out to determine the levels of exposure to PAHs from representative human diets, and the proportion of the overall burden of environmental exposure to PAHs that is attributable to the diet. In most cases, it is concluded that diet is the major source of human exposure to PAHs. The major dietary sources of PAHs are cereals and vegetables, rather than meat, except where there is high consumption of meat cooked over an open flame. More recently, biomonitoring procedures have been developed to assess human exposure to PAHs and these have also indicated that diet is a major source of exposure. Exposure to nitro-PAHs through food consumption appears to be very low.     

Bracken carcinogens in the human diet.

The ubiquitous bracken fern (genus Pteridium) is the only higher plant known to cause cancer naturally in animals. In addition to the well-recognized syndromes of thiamine deficiency, acute haemorrhage associated with myeloid aplasia and blindness due to retinal degeneration, it causes neoplasia of the urinary bladder and in some circumstances, of the upper gut. In addition, it has been shown to cause neoplasia in a wide range of tissues in many experimental species. The major carcinogen (and the cause of the retinal degeneration and the myeloid aplasia) has been shown to be ptaquiloside (PT), a norsesquiterpene glucoside that can be present in bracken in extraordinary concentrations, up to 13 000 ppm. The highest concentrations were found in the crosiers and young unfolding fronds. The mutagenicity, clastogenicity, teratogenicity and carcinogenicity have been convincingly demonstrated. Under alkaline conditions the loss of the glucose gives rise to the formation of a dienone intermediate which possesses a highly reactive cyclopropyl ring capable of reacting with cellular macromolecules. PT has been shown to alkylate DNA at N3 of adenines in the minor groove, preferentially in 5'-TAG and 3'-A in 5'-AA-3' sequences. It also alkylates N7 guanines in the major groove occurring in 5'-TG sequences. It is believed that these alkylations lead to mismatch repair and subsequent mutations in particular proto-oncogenes. Recently a rat model of carcinogenesis has been established using intravenously (iv) administered PT. Some epidemiological evidence has indicated higher risk of cancer in people who consume bracken crosiers, people who consume milk of cows feeding on bracken and those who live in bracken-infested areas. PT has been found in the milk of cows fed on bracken fern experimentally and the milk of bracken-fed cows has been shown to cause cancer in rats. PT carcinogenesis presents an excellent model of environmental and experimental carcinogenesis.     

Guar crispbread in the diabetic diet.

Nine diabetic patients who were receiving various treatments supplemented their normal home diets (two patients) or metabolic ward diets (seven patients) with guar crispbread for five days. Their mean urinary glucose excretion fell significantly by 38% during the last two days. A significant fall in fasting blood glucose concentration of 1.1 +/- 0.4 mmol/1 (19.8 +/- 7.2 mg/100 ml) was seen only in those who took guar after the control period. Over eight weeks'' treatment insulin dosage was reduced by 21% in five patients, and home testing showed that glycosuria was reduced by 68% in six patients. Guar crispbread is likely to be a useful adjunct to diabetic treatment irrespective of the type of treatment or insulin dosage used.     

Pyrrolizidine alkaloids in human diet.

Pyrrolizidine alkaloids are the leading plant toxins associated with disease in humans and animals. Upon ingestion, metabolic activation in liver converts the parent compounds into highly reactive electrophiles capable of reacting with cellular macromolecules forming adducts which may initiate acute or chronic toxicity. The pyrrolizidine alkaloids present a serious health risk to human populations that may be exposed to them through contamination of foodstuffs or when plants containing them are consumed as medicinal herbs. Some pyrrolizidine alkaloids (PA) adducts are persistent in animal tissue and the metabolites may be re-released and cause damage long after the initial period of ingestion. PAs are also known to act as teratogens and abortifacients. Chronic ingestion of plants containing PAs has also led to cancer in experimental animals and metabolites of several PAs have been shown to be mutagenic in the Salmonella typhimurium/mammalian microsome system. However, no clinical association has yet been found between human cancer and exposure to PAs. Based on the extensive reports on the outcome of human exposure available in the literature, we conclude that while humans face the risk of veno-occlusive disease and childhood cirrhosis PAs are not carcinogenic to humans.     

Quantitation of uracil in rodent diet.

Feeding of high levels of uracil to laboratory rodents results in the formation of calculi in the lumen of the urinary bladder. This urolithiasis stimulates cellular proliferation in the bladder and has been used in studies of two-stage carcinogenesis. Quantitation of uracil in rodent diet was achieved by extraction from the diet with ammonium hydroxide. The extract was applied to a strong anion-exchange solid-phase extraction column. Uracil is not retained on this matrix which adsorbs the majority of contaminants in the extract. The uracil was quantitated by HPLC on an ODS microbore column (100 x 2 mm internal diameter) eluted at 0.5 ml/min with 200 mM KH2PO4, pH 3.5, at 30 degrees C. Three structurally related pyrimidine bases, cytosine, uracil, and thymine, showed increasing retention on this column/solvent combination, thereby demonstrating selectivity of the analysis. Recovery of uracil was 76-90% with lower values observed when dietary levels of uracil were in excess of 4.5%.     

Determination of the optimum doses of nutrients in a diet.

For 14 days, SPF male Wistar rats with an initial weight of 60 g were given isocaloric diets (1.7 MJ/100 g diet) containing 10% protein (casein) and 5, 10, 25 and 40% fat (margarine). Two utilization parameters of the protein biological value--net protein utilization (NPU) and liver protein utilization (LPU)--were determined from protein intake and body and liver nitrogen. These results were supplemented by a study of the course of the antithetical processes of gluconeogenesis and glycolysis, of the citric acid cycle and transamination processes and of the liver and muscle amino acid spectrum. A high (40%) fat diet significantly reduced the protein biological value parameters NPU and LPU and liver and muscle amino acid values, stimulated gluconeogenesis and inhibited glycolysis and the citric acid cycle, together with associated transamination processes in the liver. Activation of these processes in the muscles provided substrates for increased gluconeogenesis. The negative effect of a low fat + high carbohydrate diet was less marked. The optimum diet for weaned rats is thus a diet containing 10% protein and 10--25% fat. The study, which submits several possible ways of determining optimum nutrient intakes under different physiological conditions shows that diets with more detailed nutrient concentrations should be used.     

Nutritive value of melon husk in the diet of chickens.

A study was conducted to investigate the nutritive value of melon husk (MH). Results showed that MH was low in crude protein but very high in crude fibre, ash and ether extract. The elemental analysis showed that MH was also high in calcium and phosphorus content. However, when MH was incorporated into starter diets of chicks, body weight gain decreased with increase in the level of MH in the diets. Birds fed on a 10% MH diet were superior to others in body weight gain (10.45 g/bird/day). Results of feed intake and efficiency of feed utilization were also superior on 10% MH diet with values of 43.07 g/bird/day and 4.12 recorded, respectively. The dietary treatment had significant effect (p < 0.05) on the protein efficiency ratio, which decreased with increase in level of MH in the diets. However, there appeared to be no treatment effects on haematological parameters. Up to 10% MH can replace maize in the starter diet of cockerels without adverse effect on performance.     

Comparative aspects of diet in Amazonian forest-dwellers.

Recent research shows that lowland forests of the Amazon Basin differ in numerous ways including features of climate and soils, faunal composition and forest structure, composition and phenology. Such differences strongly suggest that single-factor models used to explain features of human ecology in Amazonia may be too limited. A comparative study of the dietary ecology of four forest-living indigenous groups in Brazil (Arara, Parakana, Arawete, Mayoruna) revealed a number of differences. Primary crops, as well as animal types most utilized as prey, were found to differ markedly between groups. Although some differences can be accounted for by general environmental factors, no compelling single environmental factor can explain why any one group could not behave dietarily in ways more similar to another. Many of these intergroup dietary differences appear to represent a type of cultural character displacement that aids in distinguishing the members of one group from another. As all human groups, through the medium of culture, are actual or potential occupants of the same dietary niche, each group may distance itself from potential dietary rivals through cultural conventions. This behaviour may be justified, as the lack of overlap between forest-living groups in combination with generally intense intergroup hostility suggests that the biomass and distribution patterns of critical dietary resources in this environment may set limits to viable population size for particular areas.     

Meat meal in the diet of the early-weaned pig. II. Amino acid supplementation

One hundred and twenty pigs, initially 4–5 kg liveweight, were fed on wheat-based diets supplemented with meat meal and amino acids in two experiments, each of 4 weeks duration.In the first experiment, the supplementation of a normal meat meal diet with lysine and methionine increased the feed intake and weight gains of the pigs by 15 and 18%, respectively. Nitrogen retention was increased by 30%. Tryptophane gave a similar response to lysine and methionine.In the second experiment, a 21% crude protein basal diet was similar to the basal diet of the first experiment but it contained 1.02% lysine and 0.50% methionine plus cystine, compared to 0.90 and 0.51%, respectively, in the first experiment. Lysine and methionine supplementation of the diet did not significantly improve the performance of the pigs in the second experiment, but the supplementation of the diets with 0.08% tryptophane and lysine and methionine increased weight gains and feed intakes and decreased urea content of the blood plasma. The 21% crude protein diet contained 0.15% tryptophane.Increasing the crude protein content of diets from 18 to 24% by increasing their meat meal content increased the daily weight gains from 190 to 276 g.     

Release of bacterial alkaline phosphatase in the rumen of cattle fed a feedlot bloat-provoking diet or a hay diet.

Alkaline phosphatase (APase) was present in the bovine rumen in both cell-free and cell-associated states and levels of the enzyme varied with dietary regime. Reaction product deposition showed that the enzyme was associated with the mixed bacterial population. No enzyme was observed to be associated with protozoa. Trace activity of APase was also detected in the saliva. The presence of large amounts of APase in cell-free rumen fluid of cattle fed fine concentrate feed is believed to be due, in part, to the breakage of bacterial cells that occurs in the rumen.     

Glucosinolates in the human diet. Bioavailability and implications for health

The glucosinolates are a large group of sulphur-containing glucosides found in brassica vegetables. After physical damage to the plant tissue, glucosinolates are broken down, by the endogenous enzyme myrosinase, releasing glucose and a complex variety of biologically active products. The most important and extensively studied of these compounds are the isothiocyanates. Glucosinolates can be degraded or leached from vegetable tissue during food processing, but thermal inactivation of myrosinase preserves some intact glucosinolates in cooked vegetables. Once ingested, any remaining intact glucosinolates may be broken down by plant myrosinase in the small intestine, or by bacterial myrosinase in the colon. Isothiocyanates are absorbed from the small bowel and colon, and the metabolites are detectable in human urine 2–3 h after consumption of brassica vegetables. Isothiocyanates are potent inducers of Phase II enzymes in vitro, and they have been shown to increase the metabolism and detoxification of chemical carcinogens in vitro and in animal models. Some of these compounds also inhibit mitosis and stimulate apoptosis in human tumour cells, in vitro and in vivo. This second effect raises the possibility that in addition to blocking DNA damage, isothiocyanates may selectively inhibit the growth of tumour cells even after initiation by chemical carcinogens. Epidemiological evidence supports the possibility that glucosinolate breakdown products derived from brassica vegetables may protect against human cancers, especially those of the gastrointestinal tract and lung. To define and exploit these potentially anticarcinogenic effects it is important to understand and manipulate glucosinolate chemistry and metabolism across the whole food-chain, from production and processing to consumption. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of diet on the function of sarcoplasmic reticulum.

We have examined the effect of diet on the phospholipid composition of the sarcoplasmic reticulum of rabbit muscle. Enriching the diet with corn or fish oil results in significant changes in the fatty acyl chain composition of the various phospholipid classes, with relatively little change in the relative contents of the phospholipids. These alterations in composition have no significant effect on the ATPase activity of vesicles of sarcoplasmic reticulum or on the pattern of Ca2+ uptake and release.