High-protein, reduced-carbohydrate weight-loss diets promote adverse colonic profile

[hailtotheking]

The participants derived much of their protein from cooked meats, and there is some speculation that the problems may be related more to a high meat diet (due to the implications of high N-nitroso compounds build-up).

However, its not the first time i've read about high protein diets that are low in other macronutruents causing adverse changes in colonic environment. Certain sugars are beneficial to feeding colonic bacteria for fermentation into beneficial SCFA's, and feeding of foods containing decent SCFA and MCFA profiles provide a similar effect. Without low intake of either of these its theoretically going to cause problems in the colon in the long run.

http://www.ajcn.org/content/93/5/1062.short

Quote

High-protein, reduced-carbohydrate weight-loss diets promote metabolite profiles likely to be detrimental to colonic health

Wendy R Russell, Silvia W Gratz, Sylvia H Duncan, Grietje Holtrop, Jennifer Ince, Lorraine Scobbie, Garry Duncan, Alexandra M Johnstone, Gerald E Lobley, R John Wallace, Garry G Duthie, and Harry J Flint

+ Author Affiliations

From the Rowett Institute of Nutrition and Health, University of Aberdeen, Aberdeen, United Kingdom (WRR, SWG, SHD, JI, LS, GD, AMJ, GEL, RJW, GGD, and HJF), and Biomathematics and Statistics Scotland, Aberdeen, United Kingdom (GH).

+ Author Notes

?2 The World Cancer Research Fund played no role in obtaining or interpreting the results of this study.

Supported by the World Cancer Research Fund and the Scottish Government Rural and Environment Research and Analysis Directorate.

Address correspondence to HJ Flint, Gut Health Division, Rowett Institute of Nutrition and Health, University of Aberdeen, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, United Kingdom. E-mail: h.flint@abdn.ac.uk.

Abstract

Background: Diets that are high in protein but reduced in carbohydrate contents provide a common approach for achieving weight loss in obese humans. However, the effect of such diets on microbiota-derived metabolites that influence colonic health has not been established.

Objective: We designed this study to assess the effect of diets with reduced carbohydrate and increased protein contents on metabolites considered to influence long-term colonic health, in particular the risk of colorectal disease.

Design: We provided 17 obese men with a defined weight-maintenance diet (85 g protein, 116 g fat, and 360 g carbohydrate/d) for 7 d followed by 4 wk each of a high-protein and moderate-carbohydrate (HPMC; 139 g protein, 82 g fat, and 181 g carbohydrate/d) diet and a high-protein and low-carbohydrate (HPLC; 137 g protein, 143 g fat, and 22 g carbohydrate/d) diet in a crossover design. Fecal samples were analyzed to determine concentrations of phenolic metabolites, short-chain fatty acids, and nitrogenous compounds of dietary and microbial origin.

Results: Compared with the maintenance diet, the HPMC and HPLC diets resulted in increased proportions of branched-chain fatty acids and concentrations of phenylacetic acid and N-nitroso compounds. The HPLC diet also decreased the proportion of butyrate in fecal short-chain fatty acid concentrations, which was concomitant with a reduction in the Roseburia/Eubacterium rectale group of bacteria, and greatly reduced concentrations of fiber-derived, antioxidant phenolic acids such as ferulate and its derivatives.

Conclusions: After 4 wk, weight-loss diets that were high in protein but reduced in total carbohydrates and fiber resulted in a significant decrease in fecal cancer-protective metabolites and increased concentrations of hazardous metabolites. Long-term adherence to such diets may increase risk of colonic disease.

[emma1903]

so this is showing high protein low carb diets to not be so good for colon health but what if you did a carb up 1 day a week would this even out the effects?

[badly_dubbed]

good question.

[hailtotheking]

If there is indeed something to this theory (i.e that high protein + meat low everything else diets could be bad for colonic health), then i doubt think 6 days of high high protein + meat low everything else and one day of carbing up is going to offset that, because the diet is still 90% high protein + meat low everything else.

[emma1903]

is this study from extreme cases though like you say 90% protein and 10% everything else? most would class sub 50g a day as low carb. but are we talking sub 10-20g carbs a day as low carb? is it basically down to the lack of fibre in this kind of diet? which I'm guessing a fibre supplement could amend this?

[hailtotheking]

This is an interesting read http://arno.unimaas.nl/show.cgi?fid=16226

This part especially:

Quote

Most microorganisms prefer to ferment carbohydrate over protein and therefore saccharolytic bacterial fermentation occurs predominantly in the proximal colon, while proteolytic fermentation mainly takes place in the distal colon where fermentable carbohydrates are depleted. The latter is considered less favourable for the host because potentially toxic metabolites are formed such as ammonia, sulphurcontaining compounds, indoles and phenols. Since this distal part of the colon is the predominant location of several gastrointestinal disorders, such as ulcerative colitis and colon cancer, it could be hypothesised that the production of these toxic metabolites and a lower availability of SCFA are involved in the pathogeneses of these diseases.

[hailtotheking]

Emma, i'm guessing a decent added soluble fibre may enable fermentation in the colon to produce the required SCFA's, but i dont know for sure. Some people like Paul Jaminet have hypothesised that very low carb diets can lead to 'drying out' of the mucosal lining in the colon. Perfect Health Diet » Dangers of Zero-Carb Diets, II: Mucus Deficiency and Gastrointestinal Cancers If that was true, then even with soluble fibre the environment would not be conducive to beneficial fermentation at all

[emma1903]

oh i see so we are morely talking about an all meat diet like atkins not necessarily a low carb diet, were all carbs are sources from vegetables.

[hailtotheking]

Its difficult to say what the threshold would be before carbs got so low this might be a problem.

In the study posted in the OP, the high protein group were consuming around 22g of carbs per day and they showed problems in their colonic environment.

In Paul Jaminet's blog post, he cites examples of increased gastric disease of followers of 'The Optimal Diet', a dietary approach popularised by Jan Kwasniewski around 40 years ago who recommended that adults should eat in the ratio

60 g protein – 180 g fat – 30 g carbohydrate.

So, from these 2 examples it could be observed that anything under 30g CHO a day could cause problems.

Jaminet himself recommends a minimum of around 50g of starch-based CHO a day (i.e dont bother counting low starch veggies) if you are doing therapeutic ketogenic dieting, and preferentially around 100-125g starch CHO's per day on a maintenance diet.

[NU_nutrition_TS]

Simple answer: Low carb diets should NOT be high protein. They should be high fat - preferably with a high percentage coming from saturated fats.

The source of the protein is largely irrelevant. There have been scores of studies (largely epidemiological - therefore the caveat 'correlation does not necessarily imply causation' should apply) showing meat consumption is associated with colorectal cancer but then there are an equal amount of such studies showing there is no correlation!

If you choose to get your protein mainly from meat it does not have to be lacking in fat - you do not have to eat only lean cuts! I suspect these researchers designed these diets very much within the 'low (saturated) fat' paradigm!

It is a pity the full text of that study is not freely available - I would have liked to have seen the exact breakdown of the diet. What was the predominant dietary fat - PUFA or SFA?