Omega-3 fatty acids inhibiting the growth of a transplantable rat mammary adenocarcinoma.

BN/Bi inbred female rats fed diets containing different amounts of polyunsaturated fatty acids, either of the omega-3 or omega-6 type, each received an implant of a syngeneic mammary adenocarcinoma. When the diameter of the tumors reached 20 mm, they were surgically removed; 2 weeks thereafter the animals were sacrificed and lung metastases were counted. Cellular immune response was determined before tumor inoculation; certain prostaglandin values in plasma and platelet aggregation were measured before and after tumor inoculation. Plasma prostaglandin E2 and thromboxane B2 values were significantly decreased in those rats fed a diet containing menhaden oil. 6-Keto-prostaglandin F1 alpha, cellular immune response, and platelet function were not significantly different in either one of the diet groups. Tumor growth in the groups of rats receiving the omega-3 fatty acids in their diet was significantly inhibited in comparison with that in the rats receiving the omega-6 fatty acids. However, the number of metastases was not significantly altered.

Conversion of diets at tumor induction shows the pattern of tumor growth and metastasis of the first given diet.

In a previous study, significant differences in the growth rate of a transplantable mammary adenocarcinoma were observed between rats receiving a diet rich in saturated fatty acids (lard, diet A), and rats on a diet in which the saturated fat was partly replaced by polyunsaturated fatty acid of the omega-3 type (Menhaden oil, diet B). In the present investigation, it was our aim to study tumor growth in rats on diet A and B, as well as in rats that had, at tumor inoculation, a change of diets, from diet A to diet B. Tumor growth of rats receiving diet A throughout the whole experiment was the same as in those rats that had a conversion of diets. The data shows that the observed inhibiting effect of diet B on tumor growth could not be obtained when this diet was given exclusively after tumor inoculation.

Diets rich in fish oil cannot control tumor cell metastasis.

Rats fed diets containing different amounts of polyunsaturated fatty acids either of the n-3 or n-6 type, received cultured, syngeneic mammary tumor (BN472) cells intravenously. Animals were sacrificed 2 weeks after tumor inoculation, and the number of pulmonary tumor foci was counted. No significant differences in the number of metastatic foci were observed between the dietary groups. Prostaglandin measurements in the supernatant of tumor cells cultured in vitro showed that the tumor cells could produce thromboxane A2. Many investigators connected this tumor synthesis capacity with tumor metastatic activity. Yet in our study, diets rich in menhaden oil, with the known capacity to inhibit thromboxane synthesis, could not control tumor metastasis in this particular tumor model.

The effect of dietary carbohydrate:fat ratio on energy intake by adult women.

The effect of the dietary carbohydrate:fat (C:F) ratio on the spontaneous energy intake by healthy adults was investigated by comparing a high-carbohydrate diet (fat 24%, carbohydrate 58%, protein 18% of energy) and a high-fat diet (fat 47%, carbohydrate 35%, protein 18% of energy) in a 2 X 2 week cross-over design. Subjects were 22 healthy nuns in a Trappist convent with very regular activities. The diets consisted of combinations of liquid formula (75%) and standardized snacks (25%). The difference in C:F ratio was concealed: energy density, taste and appearance were similar. Energy consumption was recorded continuously. The mean daily energy intakes remained constant: 8276 kJ (1978 kcal). The difference in mean daily energy intake between diets was 73 kJ +/- 180 (SEM). Small changes in body weight were observed, but these are argued not to indicate definitive effects. It is concluded that changing the C:F ratio within commonly occurring ranges does not influence the spontaneous energy intake of healthy adults. The composition of the dietary fat was kept constant. Under practical conditions a change in the C:F ratio will also induce a change in the fatty acid composition of the diet, which might affect the energy intake regulation. Other experiments are required to see whether the C:F ratio can affect body composition or other physiological parameters in the long run.

The influence of increased dietary linoleate on essential hypertension in man.

A pilot study testing the hypothesis of a blood pressure lowering effect of polyunsaturated fatty acids was conducted in Evans County, Georgia. A moderate increase of dietary linoleic acid significantly decreased diastolic blood pressure in eight borderline hypertensives who were otherwise healthy, within four weeks. The change was not due to a reduced sodium content of the diet. A significant increase in creatinine excretion and clearance was noted, indicating an improvement in kidney function which might explain the blood pressure lowering effect of the fat-modified diet.

The effects of linoleic acid and prostaglandin E1 on arterial thrombosis.

The effects of dietary linoleic acid on arterial thrombus formation in rats were compared with the inhibitory effect of intravenous or intraaortic administration of PGE1, a potent inhibitor of platelet adhesion and aggregation. The "rat aorta-loop" model proved to be a useful method to induce a stable thrombus, obstructing the aortae of standard-fed rats with an obstruction time (OT) of about 96 h. Increasing the amount of dietary linoleic acid from 2.5 cal% to 30 cal% doubled OT to about 200 h. A constant intravenous PGE1 infusion of 10 mug/h increased OT significantly from the control value of 126.6 h to 160.1 h. When the same amount of PGE1 was infused intraarteriallu, the increase in OT was higher and doubled to 255.7 h. Using the "Filtragometer method" - in which platelet aggregatibility is measured in flowing human venous blood - a significant decrease in platelet stickiness was found in a group of patients consuming 12 cal% linoleic acid as compared to a similar group of patients with only 4 cal% linoleic acid in the diet. As similar results were obtained in patients with diabetes mellitus and in survivors of a myocardial infarction, increasing the amount of dietary linoleic acid may be of great therapeutic value for patients at risk of arterial thrombotic processes. These data support the hypothesis that part of the excess of dietary linoleic acid can lead to increased PGE1 concentrations.