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The influence of dietary palmitic acid triacylglyceride position on the fatty acid, calcium and magnesium contents of at term newborn faeces.

The distribution of long-chain saturated fatty acids in triglycerides is different in infant formulas to that in human milk. In human milk, palmitic acid is predominantly esterified in the sn-2 position (beta-position) of the triglycerides, whereas in infant formulas, it is esterified mainly in the sn-1,3 positions (alpha,alpha'-positions). The specific distribution of the fatty acids in the triglyceride plays a key role in lipid digestion and absorption. We studied fatty-acid, calcium and magnesium composition in the faeces of three groups of at term newborn infants fed different diets: Group A (n=12) was fed from birth to 2 months with human milk (66% palmitic acid in beta-position), Group B (n=12) was fed with formula alpha (19% palmitic acid esterified in beta-position) for 2 months, and Group C (n=12) was fed with formula alpha during the first month and with formula beta (44.5% palmitic acid in beta-position) during the second month. Samples were taken at the end of the first month (t0) and at the end of the second month (t1). Groups A and C presented significantly lower contents of palmitic acid in faeces at t1 than at t0, whereas in Group B, amounts remained similar. Faecal calcium in Groups A and C decreased in the second month (t1), although the fall was no statistically significant. In Group B, calcium amounts showed no change. We found that infant formula beta when compared with infant formula alpha reduced significantly the contents of total fatty acids and palmitic acid in faeces. We conclude that palmitic acid in beta-position is, therefore, beneficial for term infants.

Calcium↗

Absorption of oleic and palmitic acids from emulsions and micellar solutions.

A lipid mixture (monoolein, oleic acid-1-(14)C, and palmitic acid-9,10-(3)H) was infused intraduodenally at a steady rate for 8 hr in fasted, unanesthetized rats. The same dose of lipid was given together with pure conjugated bile salts either as an emulsion, 2.5 mM bile salts, or as a micellar solution, 10 mM bile salts. The emulsion contained very little or no micellar lipid. Thoracic duct lymph was collected and in some experiments bile and pancreatic juice were drained to the exterior. After 4-5 hr infusion the same steady lymphatic output of radioactive fatty acids was obtained with emulsion as with micellar solution. It was concluded that absorption of fatty acid could proceed efficiently in the virtual absence of micellar solubilization. In rats with biliary plus pancreatic fistulae, labeled triglyceride was absorbed poorly relative to free fatty acids in the same emulsified particles. This suggested that fatty acids were transferred to the absorptive cells in monomolecular solution and not as emulsion particles. Substitution of a synthetic nonionic detergent for bile salts in lipid mixtures given to rats with biliary and pancreatic fistulae did not affect the lymphatic output of radioactive fatty acids. This indicated that mucosal esterification of labeled free fatty acids was normal in the absence of bile salts. The physical state of the lipid did not affect the pathway of absorption. Finally, comparison of the increased output of esterified fat in the lymph with the output of labeled fat suggested that fat absorption did not greatly affect the turnover of endogenous, unlabeled fat. Results were consistent with the view that most of the endogenous lymph fat comes from reabsorbed biliary lipid.

Animals↗

Utilization of myristic and palmitic acid in humans fed different dietary fats.

To assess the influence of dietary fat composition on the contribution of dietary myristic and palmitic acid to total fat oxidation and energy production, eight healthy men consumed diets containing 40% of total energy as fat, largely as either butter, tallow or corn oil, for 11 days. On days 8 and 11 of each diet, [1-13C]-myristic or [1-13C]-palmitic acid (20 mg kg-1 body weight) was ingested mixed with the test breakfast meal. Respiratory gas exchange was measured before, and for 9h after, consumption of the meal. Breath 13CO2 enrichments were determined hourly by isotope ratio mass spectrometry. Cumulative 9-h percentage oxidation of dietary myristic acid exceeded that of palmitic acid (P < 0.01), but neither was influenced by fat treatment [n = 8, 7.1% (1.0) (SEM), 8.6% (0.9) and 8.9% (0.6) of dietary myristic acid and 3.3% (0.7), 3.0% (0.9), and 2.5% (0.6) of dietary palmitic acid from butter, tallow and corn oil meals respectively]. Net dietary myristic acid oxidation was greater (P < 0.05) after consumption of the meal high in butter than after consumption of other fats. Net dietary palmitic acid oxidation was similar after consumption of all test meals. Precedent fat treatment had no measurable effect on net fat or carbohydrate oxidation or energy expenditure. The overall contribution of dietary myristic or palmitic acid to total fat oxidation did not exceed 1% over 9 h for any dietary fat. These results suggest that, although dietary fatty acid content is the principal determinant of net dietary fatty acid oxidation, dietary fat sources with moderate differences in fat composition do not measurably alter total energy or substrate utilization after a meal.

Adult↗

Dietary palmitic acid influences LDL-mediated lymphocyte proliferation differently to other mono- and polyunsaturated fatty acids in rats.

Recent studies suggest that the biological effects of saturated fatty acids depend on the length of their chain. We compared the effect of diets containing different fatty acids on plasma lipids and lymphocyte proliferation in the presence of lovastatin and with increasing amounts of LDL. Lymphocytes from rats fed with a diet rich in palmitic acid had a greater lymphocyte proliferation capacity than those from rats fed with diets rich in oleic acid, linoleic acid, or fish oil. This effect was maintained when small amounts of polyunsaturatwed fatty acids (PUFA; sunflower oil) were added to the palmitic acid diet. LDL receptor activity, measured by the capacity of lovastatin to revert the inhibition of lymphocyte proliferation with increasing amounts of LDL in the medium, was greater in the rats fed with palmitic acid, and was similar to the other groups when small amounts of PUFA were added. All the groups had similar levels of plasma cholesterol, but the LDL levels were significantly lower in the group fed with palmitic acid plus PUFA. The highest HDL-cholesterol (HDLc) levels were found in the palmitic acid group and the lowest LDL-cholesterol (LDLc)/HDLc ratio in the palmitic acid plus PUFA group. These results suggest that diets rich in palmitic acid do not raise total cholesterol, but reduce LDLc or keep it normal, and raise HDLc levels. This effect may be partly due to an increase in LDL receptor activity. The inclusion of small amounts of PUFA in the diet rich in palmitic acid substantially modified the LDL receptor response in the lymphocytes, suggesting that the proportion of different families of dietary fatty acids may be more important than the individual amount of each in absolute terms to explain their effects on plasma lipids and lipoproteins.

Analysis of Variance↗

The metabolism of palmitic acid in the fetal lamb.

[1-14C]Palmitic and [9,10-3H]palmitic acids were injected into the femoral artery of fetal sheep in utero about one month preparturition. The experiment was terminated after 5, 15 or 30 min when the main tissues were removed for analysis of the lipid components. 5 min after injection of the label, most was recovered in the plasma but increasing amounts were recovered later in the liver and heart. Selective loss of 14C-label occurred such that in the plasma, 30 min after injection, the ratio of 3H:14C had changed from 1:1 to 8.4:1. Increasing amounts of the labelled lipid were recovered in esterified form with time after injection, and the 3H:14C ratio differed markedly in specific lipids and tissues. Most of the label was recovered in palmitic acid, but some was also present in myristic and octadecenoic acids. Some evidence was obtained that the latter may have been the delta 11-isomer, which was found in much greater amounts in fetal than maternal tissues. It appears that partial-oxidation and resynthesis of fatty acids occurs in a concerted manner at a rapid rate in fetal sheep. The phenomenon has important implications for the interpretation of the results of much previous work with fetal animals in vivo.

Animals↗