Like most things in life it is not black and white.
Since we know that the main omega 3 fatty acids in flax (linolenic acid) can be converted to DHA/EPA in the body, it's reasonable to suggest using flax oil to ensure some EPA/DHA production. The only problem is that the conversion rate of linolenic acid to DHA/EPA is pretty low. Theoretical estimates have been made at about a 25% to 35% conversion.
In a perfect world, you'd get about a 30% conversion, so each tablespoon of flax oil would provide about 2.5g of EPA/DHA: The only problem is that this conversion rate is dependent on a number of enzymes that vary from person to person and even from day to day. So it's really hard to estimate exactly how much DHA/EPA you'll get from using flax oil. Still, I believe that flax oil is a great source of omega 3 fatty acids when used in conjunction with salmon, or some other fish oil and/or concentrated DHA/EPA supplementation.
Once you factor in your flax oil and salmon consumption and you still need more EPA/DHA, you can purchase a concentrated EPA/DHA supplement. Some of the best and most convenient contain 0.5 - 1 g of DHA/EPA per capsule. With all of these options, it should be easy to get your DHA/EPA each day.
However, your letter indicated that you were concerned about flax oil in particular. So let's talk about the 'nads and Testosterone production. The study you mentioned was published this year by a urology research team at Duke university (Urology 2001 Jul;58(1):47-52). What the researchers did was take 25 men with prostate cancer and lower the amount of fat in their diets to about 20 percent (or less) of total calories.
In addition, they added 30 g of flaxseeds to the diet, not flaxseed oil! What the researchers found was that at the end of about 1 month, total cholesterol was lowered (from 200 mg/dl to about 170 mg/dl) as was total Testosterone (from 420n g/dl to 360 ng/dl) and the free androgen index (from 36% to 29%). In addition, some markers of prostate biology were altered.
What does this mean? Well, for starters, the decreases in Testosterone were small, especially when you consider that the range of normal Testosterone values span from 300 ng/dl to 1100 ng/dl. A decrease of 60 points in an 800-point spread between 300 and 1100 ng/dl isn't very big. While not ideal, I doubt these decreases in Testosterone would have any impact on their manhood, if you know what I mean.
In addition, low-fat diets themselves are often associated with decreases in Testosterone levels, so I propose that the lowering of fat in the diet may have caused this small drop rather than the addition of flaxseeds. In fact, several other studies have helped validate this speculation (Food Chem Toxicol 2000 Apr;38(4):325-34, J Toxicol Environ Health A 1999 Apr 23;56(8):555-70, Am J Clin Nutr 1999 Mar;69(3):395-402).
Although the first two studies mentioned were done in rats, the first of the two showed that in male rats exposed to flaxseed during gestation and weaning, Testosterone and LH levels were increased. In addition, the second study showed that rats fed a diet high in flaxseed raised Testosterone levels. And finally, in the last study, 29 humans were given a diet containing 20 g of defatted flaxseeds per day. This study showed no changes in androgen or estrogen indices.
So it's my opinion that neither flax oil nor flaxseeds will decrease your Testosterone levels. In fact, supplementing your diet with these two products may actually increase your Testosterone production. And if T doesn't even change one bit, you still have the benefits of flax oil discussed above. Adding flax seeds to the diet increases dietary fiber and the lignan content of the flaxseeds may be active in the prevention of cancer, antagonism of estrogen receptors, antioxidant protection, and increasing good blood fats (HDL) while decreasing bad blood fats (LDL and cholesterol).
So my advice is as follows: keep up the flax oil supplementation, throw some flax seeds into your diet, and finally, add some salmon.
Another common question I get is "How much flax oil should I take?" The answer to that all depends on how much fat you want in your diet. If you're trying to get bigger and eat a 30% fat diet, then you probably want 10-15% of your calories to come from oils like flax and fish oil. So at 3000 calories per day, 1000 calories should come from fat. Between 300-450 of those calories should come from polyunsaturates. That translates into about 30-50 percent of fat from salmon, flax oil, and flax seeds per day. And don't forget to add up your DHA/EPA and supplement with them as necessary to reach 6-10g per day.