The balance between dietary carbohydrate and protein has been suggested to influence gut fermentation. Negative effects on gut health might be expected if less carbohydrate and more protein reach the large intestine, due to shifts in short chain fatty acid (SCFA) (1) patterns and the formation of potentially carcinogenic N-nitroso compounds (NOC) (2) . Nonetheless, high-protein lowcarbohydrate diets are popular weight loss regimes. The aim of this study was therefore to assess the impact of

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... s with varying carbohydrate, protein and energy contents on colonic fermentation products (SCFA) and endogenous formation of NOC. We conducted a dietary intervention in 18 obese men comparing a body weight maintenance diet (448 ± 50 g/d carbohydrate, 115 ± 13 g/d protein, 13·1 ± 1·4 MJ/d energy) and three weight loss diet (9·0 ± 1·1 MJ/d) containing different levels of carbohydrate (219-308 g/d) and protein (80-156 g/d) to assess the effect of various carbohydrate and protein components. Dietary intakes were estimated from food diaries and faecal fermentation products and NOC were determined as described previously (2) .