Butyrate is an important substrate for maintenance of colonic health and oligofructose fermentation by human faecal bacteria can increase butyrate production in vitro. However, oligofructose appears to be fermented by mainly acetate and lactate-producing bacteria rather than butyrate-producing bacteria. Isotope labelling studies using [U-13C6]glucose were used to show that 13C2 and 13C4 were the major labelled butyrate species produced from glucose fermentation, via [13C2]acetate–acetyl CoA as intermediate. Bacterial interconversion reactions were quantified and acetate conversion to butyrate and lactate conversion to acetate, propionate and butyrate were observed. Addition of oligofructose to faecal batch cultures significantly increased butyrate production. Of the newly synthesised butyrate from oligofructose fermentation, 80% was derived from interconversion of extracellular acetate and lactate, with acetate being quantitatively more significant. Carbohydrates, such as oligofructose, have prebiotic properties. In addition, oligofructose selectively stimulates the bacterial conversion of acetate and lactate to butyrate. Carbohydrates with similar properties represent a refinement of the prebiotic definition, termed butyrogenic prebiotics, because of their additional functionality.

The disease-programming effects of a maternal low-protein (MLP) diet in rat pregnancy have been suggested to be attributable of hyperhomocysteinaemia. The aim of the present study was to determine whether MLP feeding impacted upon maternal and day 20 fetal homocysteine concentrations, with ensuing effects upon oxidan/ntioxidant status. Sixty-four pregnant rats were fed either MLP diet or control diet before termination of pregnancy at days 4, 10, 18 or 20 gestation (full-term gestation 22d). Maternal plasma homocysteine concentrations were similar in control and MLP-fed dams at all points in gestation. Fetal plasma homocysteine was similarly unaffected by MLP feeding at day 20 gestation. Activities of superoxide dismutase and glutathione peroxidase were similar in livers of mothers and fetuses in the two groups. Whilst catalase activity was not influenced by diet in maternal liver, MLP exposure increased catalase activity in fetal liver at day 20. Oxidative injury (protein carbonyl concentration) was lower in the livers of MLP-fed animals at day 18 gestation (P<0·05), but significantly greater at day 20. Hepatic expression of methionine synthase was similar in control and MLP-fed dams at all stages of gestation. Expression of DNA methyltransferase 1 in fetal liver was altered by maternal diet in a sex- and gestational age-specific manner. In conclusion, MLP feeding does not impact upon maternal or fetal homocysteine concentrations prior to day 20 gestation in the rat. There was no evidence of increased oxidative injury in fetal tissue that might explain the long-term programming effects of the diet.

Previous research indicates that vegetables yield relatively high satiety scores, and that fibre content and structure may both contribute to these effects. This study evaluated the effects of the fibre content and physical structure (gross anatomy and cell structure) of carrots on postprandial satiety and subsequent food intakes when consumed as part of a mixed meal. Using a randomised, repeated-measures, within-subject cross-over design, young women consumed a standardised breakfast and test lunches on three occasions, 4 weeks apart. The test lunches (3329kJ) comprised boiled rice (200g) with sweet and sour sauce (200g) that included chicken (200g) and carrots (200g) in three conditions: whole carrots (fibre and structure; n 34), blended carrots (fibre but no structure; n 34) or carrot nutrients (no fibre or structure; n 32). The carrot nutrients had the same energy, major nutrients and portion weight as the other two conditions. Post-lunch satiety was assessed by visual analogue scales. Intakes were covertly weighed at a meal eaten ad libitum (3h later), and for the remainder of the day using food diaries. Compared with the meal with carrot nutrients, meals with whole carrots and blended carrots resulted in significantly (P<0·05) higher satiety. There were significant (P<0·05) differences between conditions in intakes at the meal eaten ad libitum and for the remainder of the day, and intakes consistently decreased in the order: carrot nutrients, blended carrots, whole carrots, indicating that both fibre content and structure played a role in these effects.

Two studies have examined the effect on energy intake and macronutrient selection of increasing increments of mandatory high-fat or high-sugar snacks into the diet in men. The present study used a within-subject, repeated-measures design. In each experiment, six lean and six overweight, unrestrained men were each studied over three 7d treatment periods, during which they were given mandatory snacks of the same energy density (550k/00g) comprising the following (in terms of percentage energy as fat–carbohydrate–protein): high-fat, 80:10:10; high-sugar, 10:80:10, of which 65% was sugar, and 15% starch. Subjects were given 0, 1·5 or 3·0M/ snacks, in a randomised counterbalanced design, to be consumed mid-morning and mid-afternoon. Throughout each day, subjects had access ad libitum to fifteen high-protein, fifteen high-fat and fifteen high-carbohydrate foods, rotated on a 3d menu. Mandatory high-fat snacks significantly elevated energy intake and fat intake, whereas high-sugar snacks elevated energy intake and carbohydrate intake (all P<0·02). Mandatory increases in sugar intake did not displace fat from the diet or vice versa. It was concluded that the ingestion of up to 3M/ high-fat and high-sugar foods promoted weak compensation (18% and 30%, respectively) and therefore elevated daily energy intake by approximately 2·0–2·5MJ.