8 minute read
Gut health: research
diet SwAP
ursula Arens writer; nutrition & dietetics
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Ursula has spent most of her career in industry as a company nutritionist for a food retailer and a pharmaceutical company. She was also a nutrition scientist at the British Nutrition Foundation for seven years. Ursula helps guide the NHD features agenda as well as contributing features and reviews.
a study in swapping the diets of 20 rural africans with the equivalent number of americans for two weeks, led to some surprising results…
A year ago, it was a great day for some 20 rural Africans living near the town of Empangeni in Kwa Zulu Natal South Africa. Some American researchers asked (paraphrased), “Would you like to eat an American diet (for free) for two weeks?” The answer could only be an enthusiastic yes, even when the priceto-be-paid, the butt-clenching procedure of colonoscopy, was revealed. At the opposite end of the globe, for some 20 African-Americans living in Pittsburgh Pennsylvania there was perhaps less appeal for the offer of the diet swap experiment; an all-you-can-eat typical African diet, but with perhaps the benefit of better health.
The study of the diet swap between 20 rural Africans and 20 big-city Americans for the modest period of two weeks gained much interest in the media when published in April 2015, and mostly because there was astonishment about the speed of change to gut measures. Was a change of diet really such a fast-acting modifier on the colonic environment? It appears so. Lead researcher Professor O’Keefe, from the Department of Medicine and the University of Pittsburgh, concluded that the diet swap resulted in remarkable reciprocal changes in both groups in many of the colonic mucosal biomarkers of cancer risk (3).
Colon cancer rates are more than 13fold higher in African Americans compared to rural South Africans, and differences in diet are likely to be the main factor. American diets are high in fat and animal protein and low in fibre and a typical African diet features the inverse. But are the risk factors associated with differences in disease rates, long-term and cumulative effects from life-long dietary patterns? Or can modifications of diet result in near-instant measurable changes to gut environments?
The typical African American diet would be familiar to many British dietitians; lots of prepared meat items such as hamburger, hotdogs, ribs or steak married to lots of refined and fatty starch, such as fries, white pasta or fried potato. Colour on a plate is more likely from ketchup or mustard than fruits or vegetables. The typical rural South African diet is small embellishments around the central base of phutu/mielie meal (also called pap or very confusingly and perhaps ironically, ‘African salad’) (2). This polenta-like staple may have very small additions of vegetables or fermented milk for flavour, but the only other usual additions to the diet are beans and cabbage/onion/spinach. Fruits may be seasonally available (bananas/ pineapple/guava), but these will only be occasional items, along with salad items such a tomatoes. Chicken, meat and sausages are much relished and appreciated, but are generally considered expensive foods for special days.
After assessment for general good health and absence of exclusion criteria, 20 Americans and 20 Africans did a diet swap. The subjects were all middle aged (mean = 55 years) and most were overweight (mean BMIs = 28), although the Africans were shorter and lighter than the Americans. Diet were carefully prepared and measured and intakes observed: amounts consumed were ad libitum, but small additions of juice were added in situations where weight loss was observed in the two-week period.
uS usual diet African usual diet uS swap diet African swap diet
Energy kcals fat %E CHo %E Protein %E fibre g
2,393 35 47 15 14
2,353 16 2,205 16 72
70 11
14 66
55
2,526 52 21 27 12
The overall weight of all foods consumed by the Americans on the swap diet was bulky: it was nearly 2,300g compared to the denser 1,550g consumed by the Africans celebrating US-style cuisine.
The Africans enjoyed foods such as sausages and pancakes, or bacon and cereal for breakfast, hamburger with fries or meatballs with spaghetti for lunch and steak with noodles or roast beef and potatoes for supper. The Pittsburghers had to get used to consuming a lot of maizemeal based items. Breakfast could be maize porridge or corn grits with scrambled egg. Lunch could be maize bread with kale salad or bean soup. Supper could be maize muffins with vegetables or lentils and rice. Because maize meal is bland-tasting, a challenge was for the Americans to consume enough of this food and spice flavourings or artificial sweeteners were permitted additions.
Nutrient patterns in the swapped diets were very different. For the African-Americans, there was a reduction in energy intake due to significant reductions in fat. There were strong increases in energy from carbohydrate and fibre intakes increased nearly four-fold. For the African-Africans, the swapped diets were higher in energy diet to significant increases in intakes of fat and of protein; in fact protein intakes were considerably higher than usual American diets indicating perhaps a carpe diem attitude to the offers of luxury items such as steak and chicken. Fibre intakes in the swap diet for Africans was low; less than one fifth of their usual intakes. Intakes of a particular type of fibre, resistant starch, was calculated to be particularly high in the usual African diet and calculations from carbohydrate malabsorption of mielie meal have suggested that at least 10 percent of this food resists digestion.
Data was then collected from colonoscopy undertaken before and after the diet swap. Initial investigations found normal mucosal scores for four of the Americans (10 of the Africans). Adenomatous polyps were observed in nine of the Americans (none of the Africans). And diverticula could be observed in 14 of the Americans (but none of the Africans). Some of the markers of mucosal inflammations were higher in the Africans indicating, perhaps, higher levels of contact with parasites; two subjects were positive for schistosoma and one subject was host to a 6.0cm section of tapeworm.
There were also profound differences in the baseline microbiota of the two sample groups; Americans were dominated by the genus Bacteroides and the Africans dominated by the genus Prevotella. Professor O’Keefe characterised the African microbiota as containing more ‘starch degraders, carb fermenters and butyrate producers’ than the resident populations of the American colon.
Mucosal proliferative biomarkers of cancer were measured and were found to be significantly reduced in the US subjects following the swap diet and significantly increased in the African subjects. Further, protective faecal short chain fatty acids (acetate/ proprionate and butyrate) were increased in the US subjects and conversely reduced in the African subjects. Lastly, there was suppression of secondary bile acid synthesis in the US subjects and increased production in African subjects. Together, all of the markers in the American subjects after adoption of the rural African diet are considered as protective in relation to the risk of colon cancer (and the exact reverse in the Africans after the swap to a US diet).
concluSIonS What conclusions can be drawn from this very small and very short-term study? Are beneficial effects more due to reductions in fat or in protein, or to massive increases in fibre? Professor O’Keefe considers that the clear and measure-
able changes demonstrated in his study are remarkable, and that perhaps the next big food trend will be the ‘butyrogenic’ diet (which is, in fact, almost the inverse of the much discussed FODMAPS diet). Several large epidemiological studies have not been able to confirm associations between fibre intake and the occurrence of bowel cancer, but Professor O’Keefe suggests that there may be a threshold effect of about 50g per day (which is more than twice the current UK dietary target of 24g, and also very much higher that the proposed figure issued by the Scientific Advisory Committee on Nutrition [SACN] of 30g per day). Interestingly, the main contributors of fibre in the usual rural South African diets are not fruits and vegetable, and certainly not any wholegrain breads or cereals, rather the white stodge that is mielie-meal. And the nutritional feature of this product seems to be the high content of starch tat is resistant to digestion - perhaps up to 18 percent claim Ahmed and colleagues (1).
Eat-more-fibre has been a familiar dietary message for at least four decades and there are no obvious interests to challenge this concept. However, the conclusions from this study are that in relation to bowel health, we need a lot more and that white starchy maize can contribute significantly. This study has such a neat and tidy methodology and measured endpoints are so clear, that the small numbers and short duration do not limit the clarity of the conclusions. But the study does contribute muddle to the debates that are trying to define the components of fibre which may benefit colonic health. In seems that maize may amaze!
references 1 ahmed r, Segel I, Hassan H (2000). Fermentation of dietary starch in humans. american Journal of Gastroenterology, 2000, 95,4,1017-1020 2 engelbrecht S, de Beer T (2005). african Salad - a portrait of South africans at home. Day One publications, Cape Town 3 O’Keefe S, Li JV, Lahti L et al (2015). Fat, fibre and cancer risk in african americans and rural africans. Nature Communications DOI:10.1038/ ncomms7342
NHDmag.com DIGITAL ONLY ISSUE
Issue 104 May 2015
ISSN 1756-9567 (Online)
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