Gastrointestinal adaptation to diets of differing fat composition in human volunteers

The effect of a low fat diet (9 MJ) v a high fat diet (19.26 MJ), each consumed separately for four and 14 days, on gastric emptying and mouth to caecum transit time of a high fat test meal and body weight and satiety were examined in groups of 10 and six normal male volunteers. The half time for gastric emptying (t1/2) and the mouth to caecum transit time of a high fat test meal was significantly faster after the high fat diet than the low fat diet when consumed for 14 days (t1/2=98 (80-116) v 147 (88-206) minutes (median (range)), p less than 0.05; mouth to caecum transit time 240 (130-350) v 360 (200-520) minutes, p less than 0.05), but not when consumed for only four days. The mean (SEM) body weight of all subjects significantly increased during the 14 day high fat diet (74.7 (1.3) v 72.7 (1.6) kg, p less than 0.05) but was not influenced during the consumption of the low fat diet. When subjects were given an appetising meal to consume on the day that they had consumed the transit test meal, they ate similar amounts irrespective of their recent dietary history, though the eating rate was significantly slower after the high fat diet (mean (SEM)) 46.7 (1.9) v 71.3 (14.8)/min, p less than 0.05). Maintaining normal subjects on a high or low fat diet for two weeks resulted in a desensitisation or sensitisation respectively of the mechanisms by which nutrients regulate gastrointestinal transit. These findings emphasise the importance of the recent dietary history in the interpretation of gastric emptying and small bowel transit time data.