Satiety and energy intake after single and repeated exposure to gel-forming dietary fiber: post-ingestive effects.

BACKGROUND: Viscous or gel-forming dietary fibers can increase satiety by a more firm texture and increased eating time. Effects of viscous or gel-forming fibers on satiety by post-ingestive mechanisms such as gastric emptying, hormonal signals, nutrient absorption or fermentation are unclear. Moreover, it is unclear whether the effects persist after repeated exposure. OBJECTIVE: To investigate satiety and energy intake after single and repeated exposure to gelled fiber by post-ingestive mechanisms. DESIGN: In a two-arm crossover design, 32 subjects (24 female subjects, 21±2 y, BMI 21.8±1.9 kg m(-2)) consumed test foods once daily for 15 consecutive days, with 2 weeks of washout. Test foods were isocaloric (0.5 MJ, 200 g) with either 10 g gel-forming pectin or 3 g gelatin and 2 g starch, matched for texture and eating time. Hourly satiety ratings, ad libitum energy intake and body weight were measured on days 1 (single exposure) and 15 (repeated exposure). In addition, hourly breath hydrogen, fasting glucose, insulin, leptin and short-chain fatty acids were measured. RESULTS: Subjects rated hunger, desire to eat and prospective intake about 2% lower (P<0.015) and fullness higher (+1.4%; P=0.041) when they received pectin compared with control. This difference was similar after single and repeated exposure (P>0.64). After receiving pectin, energy intake was lower (-5.6%, P=0.012) and breath hydrogen was elevated (+12.6%, P=0.008) after single exposure, but not after repeated exposure. Fasting glucose concentrations were higher both after single and repeated exposure to pectin (+2.1%, P=0.019). Body weight and concentrations of insulin, leptin and short-chain fatty acids did not change during the study. CONCLUSIONS: Gelled pectin can increase satiety and reduce energy intake by post-ingestive mechanisms. Although the effects were small, the effects on satiety were consistent over time, whereas the effects on energy intake reduction were not.

Trans fatty acids and cardiovascular health: research completed?

This review asks the question if further research on trans fatty acids and cardiovascular health is needed. We therefore review the evidence from human studies on trans fatty acids and cardiovascular health, and provide a quantitative review of effects of trans fatty acid intake on lipoproteins. The results show that the effect of industrially produced trans fatty acids on heart health seen in observational studies is larger than predicted from changes in lipoprotein concentrations. There is debate on the effect of ruminant trans fatty acids and cardiovascular disease. Of special interest is conjugated linoleic acid (CLA), which is produced industrially for sale as supplements. Observational studies do not show higher risks of cardiovascular disease with higher intakes of ruminant trans fatty acids. However, CLA, industrial and ruminant trans fatty acids all raise plasma low-density lipoprotein and the total to high-density lipoprotein ratio. Gram for gram, all trans fatty acids have largely the same effect on blood lipoproteins. In conclusion, the detrimental effects of industrial trans fatty acids on heart health are beyond dispute. The exact size of effect will remain hard to determine. Further research is warranted on the effects of ruminant trans fatty acids and CLA on cardiovascular disease and its risk factors.

The effect of conjugated linoleic acid, a natural trans fat from milk and meat, on human blood pressure: results from a randomized crossover feeding study.

Cis-9, trans-11 conjugated linoleic acid (CLA) is a natural trans fatty acid that is largely restricted to ruminant fats and consumed in foods and supplements. Its role in blood pressure (BP) regulation is still unclear. We examined the effect of cis-9, trans-11 CLA on BP compared with oleic acid. A total of 61 healthy volunteers were sequentially fed each of 3 diets for 3 weeks, in random order, for a total of 9 weeks. The diets were identical except for 7% of energy (18.9 g in a diet of 10 MJ day(-1)) that was provided either by oleic acid, by industrial trans fatty acids or by cis-9, trans-11 CLA. We measured BP on two separate days at the end of each intervention period. At baseline, mean BP was 113.8±14.4 mm Hg systolic and 66.3±9.6 mm Hg diastolic. The effect of the CLA diet compared with the oleic acid diet was 0.11 mm Hg (95% confidence interval: -1.27, 1.49) systolic and -0.45 mm Hg (-1.63, 0.73) diastolic. After the industrial trans fatty acid diet, the effect was 1.13 mm Hg (-0.25, 2.51) systolic and -0.44 mm Hg (-1.62, 0.73) diastolic compared with the oleic acid diet. Our study suggests that short-term high intakes of cis-9,trans-11 CLA do not affect BP in healthy volunteers.

A high intake of conjugated linoleic acid does not affect liver and kidney function tests in healthy human subjects.

Conjugated linoleic acid (CLA) is consumed widely as a supplement. It causes hepatomegaly in animals, but toxicological data in humans are limited. We therefore studied the effect of a high daily intake of CLA on liver and kidney function in healthy subjects. Twenty subjects received 14.6 g cis-9,trans-11 CLA and 4.7 g trans-10,cis-12 CLA isomers a day for 3 weeks. Liver and kidney function was measured at 0, 3, 7, 10, 16, and 21 days. Mean values of all tests remained within normal limits. Lactate dehydrogenase (mean+/-SD) increased from 290.9+/-43.6 to 322.5+/-60.7 U/L (p=0.04) on day 21. One subject exceeded the upper limit of normal of 450 U/L on day 21, to 472 U/L and another showed an isolated elevation to 555 U/L on day 7. Gamma-glutamyltranspeptidase increased from 12.1+/-5.9 to 13.5+/-6.2U/L (p=0.002). No one exceeded the upper limit of 50 U/L for men and 40 U/L for women. A daily intake of 19.3 g CLA for 3 weeks does not produce clinically relevant effects on markers of liver and kidney function in healthy volunteers.