Nutrients in diet and plasma and risk of in situ cervical cancer.

Both plasma and dietary measures of vitamin A status were investigated along with previously established risk factors (number of sexual partners, age at first intercourse, smoking, and oral contraceptive use) in a study of 117 in situ cervical cancer patients and 196 matched community controls in Sydney, Australia. Neither total calories nor retinol from foods was related to cancer risk, nor was plasma retinol. When plasma and dietary indexes were considered together, vitamin C, fruit juices, and plasma beta-carotene showed protective effects. Plasma beta-carotene reduced risk from top to bottom quartile by 80%, vitamin C by 60%, and fruit juices by 50%. Thus the evidence suggests that cancer risk is associated with some aspect of diet that is reflected in the effect of plasma beta-carotene. There is no clear effect of any one nutrient but fruit juices appear protective. Thus vitamin C and beta-carotene are likely candidates.

Some problems with Cochrane reviews of diet and chronic disease.

The sum of evidence-based nutrition has to be more than a Cochrane-type meta-analysis of randomised controlled trials (RCTs). Most of the evidence base in nutrition is observational, especially cohort studies. RCTs of diet change through to disease outcome are uncommon and the change has usually been addition or removal of only a single food component. Trials with whole diets through to disease outcome are rare and dietary changes made by individuals are unlikely to be an exact copy of the prescription. It is hard to even imagine a trial in which half (randomised) of a large group of middle-aged people agree to avoid vegetables for 5 y and be followed up to see who will develop cancer. Most of the USA's health claims, permitted by the Food and Drug Administration, are not supported by RCTs. But where controlled trials of nutritional change and disease outcome have been achieved, they must be reviewed very carefully. Two Cochrane reviews on diet and cardiovascular disease (CVD), published in the widely read British Medical Journal (BMJ), were criticised after their publication and the conclusions have not been subsequently adopted by expert committees. The first of these reviews was 'Dietary fat and prevention of CVD: a systematic review'. The second was 'Systematic review of long term effects of advice to reduce dietary salt in adults'. A critique of these two Cochrane reviews is presented here as a contribution to our discussion of the potential of Cochrane methodology to the reliability of knowledge about diet and disease.

The A2 milk case: a critical review.

This review outlines a hypothesis that A1 one of the common variants of beta-casein, a major protein in cows milk could facilitate the immunological processes that lead to type I diabetes (DM-I). It was subsequently suggested that A1 beta-casein may also be a risk factor for coronary heart disease (CHD), based on between-country correlations of CHD mortality with estimated national consumption of A1 beta-casein in a selected number of developed countries. A company, A2 Corporation was set up in New Zealand in the late 1990s to test cows and market milk in several countries with only the A2 variant of beta-casein, which appeared not to have the disadvantages of A1 beta-casein. The second part of this review is a critique of the A1/A2 hypothesis. For both DM-I and CHD, the between-country correlation method is shown to be unreliable and negated by recalculation with more countries and by prospective studies in individuals. The animal experiments with diabetes-prone rodents that supported the hypothesis about diabetes were not confirmed by larger, better standardised multicentre experiments. The single animal experiment supporting an A1 beta-casein and CHD link was small, short, in an unsuitable animal model and had other design weaknesses. The A1/A2 milk hypothesis was ingenious. If the scientific evidence had worked out it would have required huge adjustments in the world's dairy industries. This review concludes, however, that there is no convincing or even probable evidence that the A1 beta-casein of cow milk has any adverse effect in humans. This review has been independent of examination of evidence related to A1 and A2 milk by the Australian and New Zealand food standard and food safety authorities, which have not published the evidence they have examined and the analysis of it. They stated in 2003 that no relationship has been established between A1 or A2 milk and diabetes, CHD or other diseases.

Low-glycemic index foods improve long-term glycemic control in NIDDM.

OBJECTIVE: To compare high- and low-glycemic index (GI) diets in the treatment of non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS: Sixteen subjects with well-controlled NIDDM and normal lipid profile, 10 of whom continued oral hypoglycemic medication, participated in the study. A diet that emphasized low-GI foods (e.g., porridge, pasta) was compared with a high-GI diet (e.g., processed cereals, potatoes). The GI of the low-GI diet was 15% lower than the high-GI diet (77 +/- 3 vs. 91 +/- 1) but otherwise similar in macronutrient composition and fiber, as determined by a 4-day weighed record. The diets were instituted under instruction from a dietitian who visited subjects at home on a weekly basis. Body weight was maintained within 1-2 kg. RESULTS: Glycemic control was improved on the low-GI diet compared with the high-GI diet (statistically significant findings, P less than 0.05). Mean glycosylated hemoglobin at the end of the low-GI diet was 11% lower (7.0 +/- 0.3%) than at the end of the high-GI diet (7.9 +/- 0.5%), and the 8-h plasma glucose profile was lower (area under the curve above fasting 128 +/- 23 vs. 148 +/- 22 mmol.h-1.L-1, respectively). Mean fasting plasma glucose, total cholesterol triglycerides, and lipoproteins did not show important differences. CONCLUSIONS: A low-GI diet gives a modest improvement in long-term glycemic control but not plasma lipids in normolipidemic well-controlled subjects with NIDDM.

Food carbohydrates and plasma lipids--an update.

An increase in dietary energy from carbohydrates is usually associated with a moderate increase in fasting plasma triglycerides--but not cholesterol--in the first weeks after the change. In the long-term the triglyceride returns to or to near the original concentration. Ordinary intakes of sucrose or fructose do not have any special elevating effect on plasma triglycerides in most normal and diabetic people, provided energy balance is not changed. Although biochemical theory predicts that fructose is more lipogenic than glucose, nearly all the animal reports of elevated plasma lipids with sucrose- or fructose-rich diets were obtained with diets unnaturally high in these sugars, and in rats and not other species. In humans, increased (fasting) triglycerides are observed with very high intakes, > 35% of energy from sucrose or > 20% of energy from fructose, and even then triglyceride elevation is unlikely unless the subjects are male and dietary fat is saturated. In people with hypertriglyceridemia (type IV), reduction of percent dietary carbohydrate is not recommended; this implies a higher percent of energy from fat, which leads to higher daylong triglycerides. However, in a minority of these patients, reduction of refined sucrose (or fructose) may be followed by lower triglycerides. Epidemiologically, high carbohydrate intakes are associated with low plasma cholesterol and variable plasma triglyceride concentrations.

Family physicians and patients: is effective nutrition interaction possible?

This article summarizes presentations from an international workshop held in Heelsum, Netherlands, 14-16 December 1998 that was sponsored by the Dutch Dairy Foundation on Nutrition and Health, the Department of Nutrition at Wageningen Agricultural University, the Dutch College of General Practitioners, and the International Union of Nutritional Sciences. Twenty-one speakers and 12 other participants were invited from 9 countries: the Netherlands, the United States, the United Kingdom, Australia, Canada, Denmark, New Zealand, Spain, and Sweden. The workshop was chaired by GJAJ Hautvast and the scientific secretary was GJ Hiddink. Family physicians are highly trusted. Many consultations include a nutritional aspect, but physicians do not discuss nutrition with their patients as often as they could. Major barriers include short visit times, the paucity of nutrition teaching in medical schools, and poor compliance of patients with physicians' dietary prescriptions. Problems, practicalities, operational research, and some solutions were discussed at this meeting of leading family doctors with interested nutritionists. Family physicians have to distill the essentials for their patients from many different specialties ranging from ophthalmology to podiatry. They look for clarity of recommendations from nutrition researchers. Among developments discussed at the meeting that can increase nutritional work in family medicine are 1) new opportunities to teach nutrition in vocational training programs, 2) some manuals and a new journal specially written by nutritional scientists for family physicians, 3) nutritional advice being incorporated into computer software for family physicians, 4) more dietitians working with family physicians, and 5) nutrition training for practice nurses in some countries.

Practical and realistic approaches to healthier diet modifications.

Nutrition research cannot improve people's health until the results influence their purchases and consumption of food and drink. There is much noise in the food information system. The most efficient solution to the problem of insufficient or conflicting public information is for all the data to be critically evaluated by a well-balanced expert committee convened by an authoritative body to produce dietary guidelines for wide publication. Such guidelines in different countries have many similar elements. Guidelines cannot be revised every year, but should be adapted only in response to major new research findings rather than to reports about nutrition in the media, which are no more than trivial distractions. The problems of family physicians giving one-on-one nutritional advice are discussed. For public health nutrition work, dietary guidelines have a range of products such as food guides and health claims on foods that are the tools of nutrition education. In developed countries, consumption of some foods has changed along with the guidelines; consumption of other foods has not. Coronary artery disease mortality has declined but obesity has increased. A more food-based approach to nutrition education is to use ideal diets as the model, such as the traditional Mediterranean diet, Japanese diet, or "hunter-gatherer" diets. These ideal diets would then need to be adapted to our present food preparation technology.

Serotonin precursor influenced by type of carbohydrate meal in healthy adults.

We compared the effects on the ratio of plasma tryptophan to large neutral amino acids (trp:LNAA) of two different carbohydrate meals (sucrose or starch, 120 g) and a contrasting meal of fat + protein given at breakfast to 10 healthy adults. Plasma glucose and insulin were also measured. The trp:LNAA ratio rose after both carbohydrate meals (p less than 0.001). Glucose and insulin peaks were higher after sucrose than starch, and trp:LNAA rose correspondingly higher (sucrose +34% and starch +20%, p less than 0.05). The ratio declined 45% after the fat + protein meal. At 180 min, absolute ratio values were twofold higher after carbohydrate (sucrose 0.133 and starch 0.127) than after fat + protein (0.057). Similar results were found with the same meals given in the evening. Our results suggest that high-carbohydrate meals have an influence on serotonin synthesis. We predict that carbohydrates with a high glycemic index would have a greater serotoninergic effect than carbohydrates with a low glycemic index.

The effect of rolled oats on blood lipids and fecal steroid excretion in man.

Rolled oats (125 g daily) were substituted for breakfast cereals and wheat flour in the metabolically controlled diets of 10 subjects for 3 wk. Fat and energy intakes in the 2-wk control periods before and after the oat period were adjusted by addition of an oil with a similar fatty acid composition to the lipid in the oats. Plasma total cholesterol concentrations were reduced in seven of 10 subjects, but over the whole group the mean reduction of 8% was not significant (0.05 less than p less than 0.01). High-density lipoprotein cholesterol concentrations and plasma triglyceride levels were unchanged. Fecal fat excretion was increased by 47% (p less 0.005) and fecal bile acid excretion by 35% (p less than 0.01) but neutral steroid excretion was unchanged on the oatmeal diet.

Effect of citrus pectin on blood lipids and fecal steroid excretion in man.

Citrus pectin (15 g/day) was added for 3 weeks to metabolically controlled diets in nine subjects. Pectin was consumed with fruit and sugar as a gel in divided doses with meals. Plasma cholesterol concentrations were reduced by a mean of 13% (P less than 0.001). Fecal fat excretion increased by 44% (P less than 0.001); neutral steroids by 17% (P less than 0.001) and fecal bile acids by 33% (P less than 0.02). Plasma triglyceride levels did not change.

Comparison of palmolein and olive oil: effects on plasma lipids and vitamin E in young adults.

Twenty-one healthy normocholesterolemic young adults, men and women, completed a randomized 30-d/30-d crossover comparison of the effect of palmolein and olive oil on plasma lipids. The subjects were free-living volunteers who changed to low-fat diets to which one of the test oils was added (used as a spread, for baking, or for frying) in turn. Complete food records were kept throughout: the test oils were compared at 17% of total dietary energy. Under the conditions of this experiment plasma total and low-density-lipoprotein (LDL) cholesterol were almost identical with the two oils, so that when the palmitic acid (16:0) in palm oil replaced oleic acid (18:1) in olive oil the expected increase in LDL cholesterol was not seen. These results indicate that 16:0, though saturated, is not always a plasma cholesterol-raising fatty acid. Palmolein is rich in vitamin E, alpha-tocopherol, and especially tocotrienols, but the latter were barely detectable in plasma.

Slowly digested and absorbed carbohydrate in traditional bushfoods: a protective factor against diabetes?

The aim of this study was to compare the digestibility and metabolic responses of western foods with traditional staples of two populations that show a susceptibility to diabetes, namely Australian Aborigines and Pacific islanders. Rate of starch digestion was studied in vitro in 37 foods (20 Australian Aboriginal bushfoods, 10 Pacific island foods, and 7 western foods), and rate of absorption of 9 foods (8 bushfoods and 1 western food) was studied in human volunteers. In vitro studies showed that 23 of 30 traditional foods were digested more slowly than 7 western foods. Six of 8 bushfoods produced significantly smaller areas under 3-h postprandial plasma glucose curves than potatoes in seven healthy Caucasian volunteers. There was a good correlation between starch digestibility and plasma glucose response. Our findings are consistent with the hypothesis that carbohydrate in traditional diets is slowly digested and absorbed and may once have been protective against diabetes.

Application of glycemic index to mixed meals.

Plasma glucose and insulin responses to six different meals were determined and compared with values predicted by published glycemic indices of the component foods. The test meals were of different ethnic origins: Indian (lentil curry with rice), Italian (spaghetti bolognaise), Chinese (stir-fried vegetables and chicken with rice), Greek (lentil stew), Western (sirloin chop and vegetables); and Lebanese (sandwich with unleavened bread and hummos). Eight healthy volunteers were given 50 g carbohydrate portions of the above meals after an overnight fast. The glycemic and insulin indices were highest for the Lebanese meal and lowest for the Greek with significant differences among the meals (ANOVA, p less than 0.05). The observed glycemic indices correlated well with the predicted glycemic indices (r = 0.88, p less than 0.01) and insulin responses parallelled the glycemic responses (r = 0.83, p less than 0.05). These results suggest that the glycemic index approach will be useful in planning diets for diabetic people.

Incomplete absorption of pure fructose in healthy subjects and the facilitating effect of glucose.

Small-intestinal absorption of fructose was investigated in healthy human subjects by sequential breath-hydrogen measurements. Fifty-eight percent of 103 subjects produced greater than 20 microL H2/L after consuming 50 g pure fructose in water. About half of those who absorbed fructose incompletely (incomplete absorbers) had abdominal symptoms. Malabsorption of medium doses of pure fructose may therefore be common in man. When 25 g pure fructose was consumed, only 19% of 21 poor absorbers (of 50 g fructose) still produced excess breath H2. When glucose was taken with fructose, the frequency and amount of excessive breath H2 was substantially reduced. This facilitating phenomenon is not generally known but is important because in natural foods fructose occurs in association or in combination (as sucrose) with glucose. Plasma fructose responses were not lower in poor absorbers presumably because these responses depend more on how much fructose passes through the liver than on how much is absorbed.

Glycemic index of processed wheat products.

Our aim was to determine the in vivo glycemic and insulin responses and in vitro starch digestibility of seven processed wheat products (shortbread biscuits, custard, quick-cooking wheat, wholemeal bread, water biscuits, puffed wheat, and puffed crispbread). The degree of starch gelatinization in the foods was measured. Fifty-gram carbohydrate portions of the foods were fed to eight volunteers after an overnight fast. The calculated glycemic indices (GI) (mean +/- SEM) ranged from 43 +/- 10 for custard to 81 +/- 9 for puffed crispbread. Insulin responses paralleled the glycemic responses. The GI correlated positively with the percentage of starch digested in vitro (p less than 0.05). The degree of starch gelatinization ranged from 0.4 to 60% and correlated positively with the percentage starch digested in vitro (p less than 0.05). Differences in the glycemic and insulin responses to wheat products may be explained in part by the extent of processing and the degree of gelatinization achieved.

Plasma glucose and insulin responses to starchy foods in Australian aborigines: a population now at high risk of diabetes.

We compared plasma glucose and insulin responses to an Aboriginal bushfood and its western equivalent in healthy Aborigines and Caucasians. Bush potato (Ipomoea costata), an Aboriginal bushfood which is slowly digested in vitro, and potato (Solanum tuberosum), which has a high glycemic index, were studied. The areas under the glucose and insulin curves for Aborigines were 34% and 42% smaller, respectively, after bush potato than after potato (p less than 0.05). In Caucasians only the insulin response to bush potato was lower (by 19%) than that to potato (p less than 0.05). Compared with Caucasians, Aborigines produced 2.5 times greater glucose and insulin responses to potato (p less than 0.025). Their insulin responses to bush potato were also twice as large (p less than 0.05) although glucose responses were not significantly different. These findings add weight to the hypothesis that rapidly digested carbohydrate in western diets may be one of the factors in the lifestyle change which precipitates diabetes in indigenous populations.

A mixed Australian fish diet and fish-oil supplementation: impact on the plasma lipid profile of healthy men.

Twelve healthy men were fed in turn three diets for 6 wk each in a 3 x 3 randomized block design: a control diet (essentially fish free), a fish diet (200 g lean Australian fish flesh/d), and the same fish-based meal but supplemented with 5 g fish oil/d. Dietary eicosapentaenoic acid [EPA, 20: 5n-3 (omega-3)] was strongly associated with erythrocyte membrane EPA (r = 0.908 at 6 wk), strengthening its value as a measure of compliance in fish and fish-oil feeding trials. On the fish diet, subjects had increased incorporation of n-3 polyunsaturated fatty acids (PUFAs) at the expense of n-6 PUFAs in their erythrocyte membranes. When the fish-based diet was supplemented with fish oil (5 g/d), there was a significant lowering of plasma triacylglycerol (-0.16 +/- 0.24 mmol/L; mean +/- SD). No change in plasma total cholesterol was detected although the fish + oil diet produced a reduction in very-low-density-lipoprotein cholesterol (-0.24 +/- 0.26 mmol/L).

Plasma glucose and insulin responses to traditional Pima Indian meals.

The in vivo glycemic and insulin responses and in vitro starch digestibility were determined for six staple foods (corn, lima beans, white and yellow teparies, mesquite, and acorns) traditionally consumed by Pima Indians. Equivalent carbohydrate portions (25 g) of the foods were fed to eight healthy Caucasian volunteers. The calculated glycemic indices (GIs) (mean +/- SEM with glucose as the standard) were all low, ranging from 16 +/- 2 for acorns to 40 +/- 5 for corn. Insulin responses and in vitro starch digestibilities correlated with the GI. These results provide further support for the hypothesis that the slow digestion and absorption of starch in traditional foods was a factor that helped protect susceptible populations from developing diabetes.

Reduction of food intake in the ovulatory phase of the menstrual cycle.

Food intake was weighed and recorded daily during one complete menstrual cycle in 18 healthy normally menstruating women. Urinary luteinizing hormone indicated the time of ovulation. Mean daily intakes of energy, macronutrients, and alcohol were calculated for five phases during the menstrual cycle: menses, postmenses, ovulatory, postovulatory, and premenses. Weekly variations were also measured. Energy intake was lowest during the ovulatory phase compared with postovulatory, premenses, and menses phases (p less than 0.05). The maximum difference, 1.36 MJ (324 kcal)/d, occurred between ovulatory and postovulatory phases and was twofold higher than the increase of 0.64 MJ (152 kcal)/d observed at weekends. This reduction of food intake at ovulation has not been previously described in humans. It coincides with the expected peak in circulating estrogen levels and is consistent with the hypothesis in animal models that estrogen is an appetite suppressant.

Food processing and the glycemic index.

The purpose of the study was to compare the in vitro starch digestibility and postprandial blood glucose response of conventionally-cooked versus factory-processed foods. Carbohydrate portions of three unprocessed foods (boiled rice, sweet corn, and potato) and six processed foods (instant rice, Rice Bubbles, corn chips, Cornflakes, instant potato, and potato crisps) were incubated for 3 h with human saliva and porcine pancreatin. The proportion of starch digested was significantly higher (p less than 0.05) for the processed forms of rice, corn, and potato compared with the respective conventionally cooked foods. In six healthy volunteers who ingested 50 g carbohydrate portions of the above foods the processed foods produced a higher glycemic index (p less than 0.05) in all but one instance. The exception was potato crisps which gave a similar glycemic response to boiled potato.