Isoleucine, like other branched-chain amino acids, is associated with insulin resistance: higher levels of isoleucine are observed in the blood of diabetic mice, rats, and humans. Mice fed an isoleucine deprivation diet for one day have improved insulin sensitivity, and feeding of an isoleucine deprivation diet for one week significantly decreases blood glucose levels. In diet-induced obese and insulin resistant mice, a diet with decreased levels of isoleucine and the other branched-chain amino acids results in reduced adiposity and improved insulin sensitivity. In humans, a protein restricted diet lowers blood levels of isoleucine and decreases fasting blood glucose levels.
The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For isoleucine, for adults 19 years and older, 19 mg/kg body weight/day.
Even though this amino acid is not produced in animals, it is stored in high quantities. Foods that have high amounts of isoleucine include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish.
Isoleucine is a branch chained amino acid (BCAA). In plants, some enzymes involved in BCAA biosynthesis are the targets of several herbicides used by farmers. Because of their importance in human and animal nutrition and agriculture, the biosynthesis pathways of BCAAs in higher plants have been extensively studied and well characterized (Singh and Shaner, 1995; Binder, 2010).
The articles on Isoleucine that I’ve read say that it exists in “higher plants” which means plants of relatively complex or advanced characteristics, especially vascular plants (including flowering plants). In plants, the conversion of threonine to 2-oxobutanoate is the first and also the committed step towards isoleucine biosynthesis. This reaction is catalysed by threonine deaminase/dehydratase (TD) (Fig. 7A).
The take from this is, if you are a vegan or want to be and would like to eat necessary amino acids from plants, find a high quality, ORGANIC source for your plant food. Grow it yourself if you can and don’t use herbicides.