The quantities of fatty acids w3 and w6 in milk are small in the context of amounts in the diet. Furthermore, the biological effect of w3s and w6s may require that these fatty acids be located in position #2 of the triglyceride (milk fatty acids are usually triglycerides, not phospholipids). Thus, from the published article it is difficult to determine whether the amounts of w3s and w6s that one can eat and translate into biological activity (e.g., membrane function or eicosanoids) are substantial or small. Most people are likely to get more w3s and w6s from other foods. Altogether, although organic milk is probably preferable to regular milk, the impact of w3s and w6s is minor. One needs to calculate the effect of drinking milk every day for 20 years or some period of time to determine how long is needed to have an effect.
Fatty acid analysis is very difficult; quantitation is subject to many technical errors. The authors should have published several sample chromatograms and description of how the peaks are integrated. They should also include the specific “method” used to separate fatty acids (temperature programming, duration, etc.) and equipment used (GLC, Mass Spec). In general, FA are injected into the Supelco column 2560 used by authors. Over the 100 cm, they separate. FA from cow’s milk, depending on the extraction method, may create 50 to 100+ peaks. Some peaks are superimposed by derivatives from the extraction method (the type of FA derivative used in the analysis), or from previous injections (retained by the column). The AOCS methods do not describe these issues explicitly enough (they are described in textbooks, professional journals and my articles).
The chromatogram has substantial baseline fluctuations (depend on the amounts injected, techniques and gases used, purity of the system, etc.). The software that integrates peaks (the usual means to quantitate substances) may get confused and improperly detect the beginning and end of peaks. Often the area around linoleic and linolenic acid are crowded (with many peaks). Each injection must be individually analyzed and reintegrated many times. It is common to have integration errors that amount to 0.5% of total fatty acids (sometimes much higher). Thus, the amount of linolenic could be smaller than the amount reported. These errors are very important in peaks with total peak area under 5% of total FA. The authors must provide chromatograms and explain how each sample was individually evaluated to minimize integration errors. Other technologies used to quantify peaks (substances) have different types of errors.
I have shown that many Americans have deficiencies of w3s and w6s. For these individuals, what matters most is likely to be total intake of w3+w6, not the ratio w3/w6. For most Americans, I suggest that the major source of disease risk (for cardiovascular disease, cancer) appears to be excessive calorie intake with a low ratio of (w3+w6)/(Other Fatty acids) (see references). Milk, overall, has a low ratio (the authors indicate that total w3+w6 = about 4% of all FAs). Milk provides a relatively high ratio of calories from all sources/calories from w3+w6. This means that milk may not be an efficient source of essential fats (w3+w6) for most individuals who already eat too many calories. Remember that calories from all sources, not used for metabolic purposes, may be stored as saturated and monounsaturated FAs. Nevertheless, it is likely that feeding cows natural foods high in essential fats will produce a healthier milk and meat.
Siguel, E. Method and Apparatus for Diagnosis of Fatty Acid or Lipid Abnormalities. U.S. Patent No. 5075101, Issue date 12/24/91.
Siguel E, Lerman, RH. Altered Fatty Acid Metabolism in Patients With Angiographically Documented Coronary Artery Disease. Metabolism 1994; 43:982-93.
Siguel E. Essential and Trans Fatty Acid Metabolism in Health and Disease. Nutrition Issue. Comprehensive Therapy, 1994; 20(9):500-10 (Review).
Siguel, E. A New Relationship between Total/HDL Cholesterol and Polyunsaturated Fatty Acids. Lipids, 1996; 31:S51-6.
Siguel E, Lerman RH, MacBeath, B. Very Low-Fat Diets for Coronary Heart Disease: Perhaps, but Which One? JAMA, 1996; 275: 1402-03. Erratum in: JAMA 1996; 276(12):954 (let).
Siguel, E. Diagnosis of EFA Abnormalities. Proceedings of the 56th Flax Institute Meeting, Fargo, ND 1996.
Siguel, E. Issues and Problems in the Design of Foods Rich in Essential Fatty Acids. Lipid Technology, 1996; 8(4):81-86 (July).
Siguel, E. Symposium on Measuring EFAs in Biological Tissue. Abstracts & Proceedings Am. Oil. Chemistry Society Annual Meeting, 1996.
Siguel E. EFA Status in Patients. J Parent.Ent.Nutr. 1997 Jul-Aug; 21(4):243 (let).
Siguel, E. Deficiencies and Abnormalities of Essential Fats in Gastrointestinal and Coronary Artery Disease. Journal of Clinical Ligand Assay 2000; 23:104–11.
Siguel, E. Clinical Impact of Methodological Issues in the Diagnosis of Deficiencies and Abnormalities of Essential Fats. Journal of Clinical Ligand Assay 2000; 23:112–21.