High a-Linolenic Acid Flaxseed (Linum Usitatissimum): Some Nutritional Properties in Humans.
High a-Linolenic Acid Flaxseed (Linum Usitatissimum): Some Nutritional Properties in Humans.
Year: 1993
Authors: S C Cunnane, S Ganguli, C Menard, A C Liede, M J Hamadeh, Z Y Chen, T W S Wolever, D J A Jenkins.
Publication Name: Brit. J. Nutr.
Publication Details: Volume 69; Page 443.
Abstract:
Flaxseed oil has traditionally been used in North America to treat diseases associated with n-3 PUFA deficiency including neurological and visual disturbances, scaly dermatitis and growth retardation. Previous studies have assessed the effects of cold-pressed flaxseed oil on serum lipids, FA composition and platelet function. However, high amounts of flaxseed oil (10 – 60 g/day) were used, levels which would be difficult to incorporate into a daily diet. These studies were also of short duration, usually 2 weeks or less. Although flaxseed appears to have very beneficial health effects, its high oil content (350 – 400 g/kg flaxseed) and polyunsaturation (720 g/kg oil) may give rise to lipid peroxides and reduce antioxidants. In a series of experiments, the authors have evaluated the nutritional value of flaxseed as a source of n-3 PUFAs and soluble fiber (60 – 80 g/kg of mucilage). The potential toxicological aspects of flaxseed were also assessed through the measurement of peroxides. Four separate experiments were conducted to determine (1): the effects of flaxseed on plasma FA and lipids, and on thiocyanate (a cyanogenic glycoside which may appear in the blood following the consumption of raw flaxseed); (2) relative changes in blood FAs after consuming flaxseed flour versus flaxseed oil containing the same amount of ALA; (3) effects of flaxseed and flaxseed mucilage on blood glucose responses, and (4) effects of baking flaxseed into muffins on the content of the lipid peroxidation product malondialdehyde (MDA) and cyanogenic glycosides. In the first study, the typical diets of healthy female volunteers were supplemented with 50 g ground, flaxseed/day for 4 weeks as either flaxseed flour (n=5) or bread baked with flaxseed flour (n=4). The flaxseed flour provided 12-13% of energy intake (24-25 g/100 g total fat). Both forms of flaxseed significantly raised ALA, EPA and DHA in both plasma and erythrocyte lipids. Urinary thiocyanate excretion was increased by about two fold. The flaxseed diets also lowered serum TC by 9% and LDL-C by 18%. No changes in HDL-C or TG were noted. Changes in plasma ALA were compared in a cross-over study in which 12 g of ALA/day was consumed as raw flaxseed flour (50 g/day) or flaxseed oil capsules (20 g/day), in the second study. Five health females consumed the flaxseed or flaxseed oil for 4 weeks in a randomized order with a 2 week wash-out period. Changes in plasma ALA were equivalent following both treatments. Total n-3 PUFAs (ALA, EPA and DHA) were significantly increased in plasma TG following the flaxseed and flaxseed oil. These results suggest a high bioavailability of ALA from ground flaxseed. In the third study, the potential of soluble fiber mucilage in flaxseed to reduce postprandial changes in blood glucose was assessed by a standardized method. Following an overnight fast, 6 healthy volunteers consumed, in random order, a test meal containing 50 g of carbohydrate as bread made from white flour or from flaxseed flour. The effect of 50 g of glucose versus 50 g of glucose mixed with 25 g of mucilage was compared over 120 minutes. The test meals containing carbohydrate from flaxseed or flaxseed- mucilage each significantly decreased postprandial blood glucose responses by 27%. In the fourth study, flaxseed was incorporated into muffins and assessed for peroxides and cyanogenic glycosides. MDA levels in muffins containing 15 g flaxseed oil or flaxseed flour/kg were similar to those in wheat-flour muffins. Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage but were not detected in baked muffins containing 150 g FS/kg. Based upon the results of the four studies, the authors concluded that up to 50 g high ALA flaxseed /day is palatable, safe and nutritionally beneficial in humans. flaxseed can raise n-3 FAs in plasma and erythrocytes, reduce serum lipid levels and decrease postprandial glucose responses, responses which appear to be due to both ALA and mucilage soluble fiber. The authors suggest the inclusion of flaxseed in the diets of hypercholesterolemic and diabetic patients.
