Effect of low-fat, high-fat, and fiber-supplemented high-fat diets on colon cancer risk factors in feces of healthy subjects

Recent Perspectives on the Relations between Fecal Mutagenicity, Genotoxicity, and Diet

DNA damage is an essential component of the genesis of colonic cancer. Gut microbial products and food components are thought to be principally responsible for the damage that initiates disease progression. Modified Ames tests and Comet assays have been developed for measuring mutagenicity and genotoxicity. Their relevance to oncogenesis remains to be confirmed, as does the relative importance of different mutagenic and genotoxic compounds present in fecal water and the bacteria involved in their metabolism. Dietary intervention studies provide clues to the likely risks of oncogenesis. High-protein diets lead to increases in N-nitroso compounds in fecal water and greater DNA damage as measured by the Comet assay, for example. Other dietary interventions, such as non-digestible carbohydrates and probiotics, may lead to lower fecal genotoxicity. In order to make recommendations to the general public, we must develop a better understanding of how genotoxic compounds are formed in the colon, how accurate the Ames and Comet assays are, and how diet affects genotoxicity.

Processed meat and colorectal cancer: a review of epidemiologic and experimental evidence

Processed meat intake may be involved in the etiology of colorectal cancer, a major cause of death in affluent countries. The epidemiologic studies published to date conclude that the excess risk in the highest category of processed meat-eaters is comprised between 20% and 50% compared with non-eaters. In addition, the excess risk per gram of intake is clearly higher than that of fresh red meat. Several hypotheses, which are mainly based on studies carried out on red meat, may explain why processed meat intake is linked to cancer risk. Those that have been tested experimentally are (i) that high-fat diets could promote carcinogenesis via insulin resistance or fecal bile acids; (ii) that cooking meat at a high temperature forms carcinogenic heterocyclic amines and polycyclic aromatic hydrocarbons; (iii) that carcinogenic N-nitroso compounds are formed in meat and endogenously; (iv) that heme iron in red meat can promote carcinogenesis because it increases cell proliferation in the mucosa, through lipoperoxidation and/or cytotoxicity of fecal water. Nitrosation might increase the toxicity of heme in cured products. Solving this puzzle is a challenge that would permit to reduce cancer load by changing the processes rather than by banning processed meat.

Nutritional associations with bone loss during the menopausal transition: evidence of a beneficial effect of calcium, alcohol, and fruit and vegetable nutrients and of a detrimental effect of fatty acids

BACKGROUND

The menopausal transition is characterized by rapid bone loss. Few data exist on the role of nutrition.

OBJECTIVE

The objective of the study was to ascertain which dietary factors influence perimenopausal skeletal loss.

DESIGN

A longitudinal study was conducted of 891 women aged 45-55 y at baseline and 50-59 y at follow-up 5-7 y later. Bone mineral density (BMD) was measured by using dual-energy X-ray absorptiometry at the lumbar spine and femoral neck (FN). Nutrient intakes were assessed after the baseline visit and 5 y later, by using the same food-frequency questionnaire.

RESULTS

After adjustment for energy intake and other confounders, higher intakes of calcium were correlated with change in FN BMD (ie, reduced loss) (r = 0.073, P < 0.05), and the intake of modest amounts of alcohol was associated with less lumbar spine bone loss (P < 0.01 for quartile of alcohol intake). Greater FN BMD loss was associated with increased intake of polyunsaturated fatty acids (r = -0.110, P < 0.01), monounsaturated fatty acids (r = -0.069, P < 0.05), retinol (r = -0.067; P < 0.05), and vitamin E (r = -0.110; P < 0.01). The latter 2 nutrients were highly correlated with polyunsaturated fatty acids. For premenopausal women, calcium and nutrients found in fruit and vegetables (vitamin C, magnesium, and potassium) were associated with FN BMD, and calcium, vitamin C, and magnesium were associated with change in FN BMD.

CONCLUSIONS

Although menopausal status and hormone replacement therapy use dominate women's bone health, diet may influence early postmenopausal bone loss. Fruit and vegetable intake may protect against premenopausal bone loss.

Meat and cancer: haemoglobin and haemin in a low-calcium diet promote colorectal carcinogenesis at the aberrant crypt stage in rats

High intake of red meat, but not of white meat, is associated with an increased risk of colon cancer. However, red meat does not promote cancer in rodents. Haemin, added to low-calcium diets, increases colonic proliferation, and haemoglobin, added to high-fat diets, increases the colon tumour incidence in rats, an effect possibly due to peroxyl radicals. We thus speculated that haem might be the promoting agent in meat, and that prevention strategies could use calcium and antioxidants. These hypotheses were tested in rats at the aberrant crypt foci (ACF) stage at 100 days. F344 rats (n = 124) were given an injection of azoxymethane and were then randomized to 11 groups fed with low-calcium (20 micro mol/g) AIN76-based diets, containing 5% safflower oil. Haemin (0.25, 0.5 and 1.5 micro mol/g) or haemoglobin (1.5 and 3 micro mol haem/g) was added to five experimental diets, compared with a control diet without haem. Three other high-haemin diets (1.5 micro mol/g) were supplemented with calcium (250 micro mol/g), antioxidant butylated hydroxyanisole and rutin (0.05% each), and olive oil, which replaced safflower oil. Faecal water was assayed for lipid peroxidation by thiobarbituric acid reactive substances (TBARs) test, and for cytolytic activity. Haemin strikingly increased the ACF size, dose-dependently, from 2.6 to 11.4 crypts/ACF (all P < 0.001). The high-haemin diet also increased the number of ACF per colon (P < 0.001). Promotion was associated with increased faecal water TBARs and cytotoxicity. Calcium, olive oil and antioxidants each inhibited the haemin-induced ACF promotion, and normalized the faecal TBARs and cytotoxicity. The haemoglobin diets increased the number of ACF and faecal TBARs, but not the ACF size or the faecal cytotoxicity. In conclusion, dietary haemin is the most potent known ACF promoter. Haemoglobin is also a potent promoter of colorectal carcinogenesis. The results suggest that myoglobin in red meat could promote colon cancer. Diets high in calcium, or in oxidation-resistant fats, may prevent the possible cancer-promoting effect of red meat.

Longitudinal changes in weight in perimenopausal and early postmenopausal women: effects of dietary energy intake, energy expenditure, dietary calcium intake and hormone replacement therapy

OBJECTIVE

To investigate whether energy intake or energy expenditure affects 5-7 y weight gain in perimenopausal and early postmenopausal women, and whether hormone replacement therapy (HRT) use or dietary calcium (Ca) intake are contributory factors.

DESIGN

Longitudinal, observational study of healthy women around the menopause.

SUBJECTS

A total of 1064 initially premenopausal women, selected from a random population of 5119 women aged 45-54 y at baseline. In all, 907 women (85.2%) returned 6.3+/-0.6 y later for repeat measurements. Of these, 36% were postmenopausal (no HRT) and 45% had taken HRT, and 898 women completed the questionnaires.

MEASUREMENTS

Weight, height, estimation of energy intake by food frequency questionnaire and physical activity level (PAL) by questionnaire.

RESULTS

Change in PAL influenced weight change explaining 4.4% (P=0.001) of the variation. Alterations in dietary energy intake also had a small but significant effect (0.6% P=0.013). Dietary Ca intake had no effect on weight or weight change.

CONCLUSION

Mean weight had increased and was influenced more by reduced energy expenditure rather than increased energy intake. HRT and dietary Ca intake did not influence weight gain.

The effect of dietary vitamin D3 on the intracellular calcium gradient in mammalian colonic crypts

A physiological gradient in intracellular calcium ([Ca2+]i) has been hypothesized to exist along the colonic crypt base-mouth axis, which may be involved in the regulation of colonocyte proliferation, differentiation and apoptosis. In addition [Ca2+]i may be modulated by dietary vitamin D3 which is thought to be protective against colorectal cancer. CF1 mice were maintained for 6 weeks on a defined diet containing either high or low vitamin D3. A colonic crypt base-mouth [Ca2+]i gradient of 201 +/- 79 nM (mean +/- SEM, P < 0.05) was observed in animals maintained on a high vitamin D3 diet and was abolished in mice maintained on a low vitamin D3 diet. The [Ca2+]i gradient was independent of extracellular calcium and elevated levels of [Ca2+]i observed in the basal regions of the crypt in animals maintained on low levels of vitamin D3 were also associated with an increase in intracellular calcium stores. Therefore, a [Ca2+]i gradient exists in colonic crypts and is dependent on dietary vitamin D3.

Effects of a high-fat diet on azoxymethane-induced aberrant crypt foci and fecal biochemistry and microbial activity in rats

To shed light on the association of dietary fat with the development of colon cancer, we studied the ability of azoxymethane (AOM) to induce aberrant crypt foci (ACF) and biochemical changes in rats fed high- or normal-fat diets. Six-week-old male Fischer 344 rats were placed on a high-fat [7% (wt/wt) soybean oil + 15% (wt/wt) beef tallow] or a normal-fat (7% soybean oil, AIN-93G) diet. Rats fed each of these diets were given two weekly subcutaneous injections of AOM (15 mg/kg body wt) or saline at seven and eight weeks of age. Fecal samples were obtained at 10 weeks of age, and animals were sacrificed for ACF scoring and analysis of cecal contents at 13 weeks of age. We observed greater numbers of ACF in the high- than in the low-fat group. Biochemically, rats fed the high-fat diet showed dramatically elevated fecal and cecal long-chain free fatty acid levels and intestinal alkaline phosphatase activity. These animals also showed increased cholesterol and decreased coprostanol levels. We did not detect significant differences in the fecal and cecal concentrations of total and soluble bile acids or total neutral sterols (cholesterol + coprostanol) between the two groups. Thus a high-fat diet does show certain striking effects on colon biochemistry in rats.

Beef tallow, but not corn bran or soybean polysaccharide, reduces large intestinal and fecal bile acid concentrations in rats

Diets high in fat and low in dietary fiber have been associated with a higher incidence of colon cancer, possibly by increasing bile acid concentration in the colon. Therefore changes in bile acid metabolism due to beef tallow, corn bran (CB), and soy polysaccharide (SP) feeding were studied. Rats were fed one of four diets for six weeks: 5% beef tallow fiber-free (LF), 20% beef tallow fiber-free (HF), 20% beef tallow with CB (HFCB), and 20% beef tallow with SP (HFSP). HF increased fecal output compared with LF, and HFCB and HFSP increased fecal output compared with HF. HF reduced fecal bile acid concentration by two-thirds compared with LF, although daily bile acid excretion was similar. There was a tendency toward a smaller bile acid quantity in the small intestine with HF than with LF. Neither fiber altered total fecal bile acid concentration or small intestinal bile acid quantity compared with HF. However, 7 alpha-dehydroxylase activity in the colon was lower with HFSP than with HFCB. Increasing dietary beef tallow from 5% to 20% in animals fed a fiber-free diet greatly reduced the concentration of bile acids in the large intestine and feces, an effect associated with a reduced risk of colon cancer.