I just finished reading large sections of your book, which I find fantastic and will highly recommend to friends. With regards to supplements, one that I take, but did not see mentioned, is conjugated linoleic acid (CLA). Any thoughts on whether this is needed in a reasonably healthy diet? I am an 80 kg, 46-year-old competitive road racer.
At this point there is no reason to add conjugated linoleic acid to a healthy diet or training diet as based on the current research. CLA has been studied fairly extensively, but mostly in animals. In these animal studies CLA appears to reduce body fat stores, while preserving lean body mass. CLA supplements are usually accompanied with photographs of the taut abdominal six-pack. Some manufacturers also promote CLA as reducing the risk for diabetes and certain types of cancer. However, whether it can do the same in humans is the still the subject of ongoing research and currently the human data is less than conclusive.
What is CLA?
You may be surprised to learn that CLA is a mixture of polyunsaturated fatty acids which are actually natural trans fats. Trans fats have received much deserved attention as the latest culprits in promoting increased levels of blood cholesterol. However, the trans fats found naturally in some foods are different than the manufactured form found in processed foods and won’t raise blood cholesterol as these hydrogenated oils can. These natural trans fat are also not included for the purposes of nutritional regulations and labeling. Food sources of CLA include animal foods like whole milk, cheese, beef, lamb, veal, poultry, and eggs.
Food products of grass fed animals are good sources and contain much more CLA than those from grain fed animals. In fact, pasture grazed cows may have 3 to 5 times more CLA in their milk than cows fed hay. There are about 28 possible types of CLA, each one with a slightly different arrangement of chemical bonds. The type most commonly found in meat and dairy products is the cis 9, trans-11 CLA form, which appears responsible for promoting muscle growth.
Another form, the trans-10, cis-12 form seems to help prevent fat storage. The average diet provides about 50 to 300 milligrams of CLA a day. Switching from grain-fed to grass-fed products can greatly increase your CLA intake. Because many sources of CLA are also high in saturated fat and increase your risk for heart disease, the best way to boost your CLA dietary intake is to switch from grain-fed to grass-fed products.
Supplements often contain manufactured sources of CLA, so they likely contain fatty acids different from these natural sources, but many do contain a mix of the these two forms mentioned above. There is still some debate about which of the fatty acids are really the most beneficial, so whether a manufactured supplement is as good as natural CLA or which supplement is the best has not been conclusively determined.
Dozens of animal studies conducted over two decades have established that CLA can dramatically reduce body fat stores, while preserving lean muscle mass. Animal studies have also found that CLA may protect against certain types of cancers. Human data is far less conclusive. Several clinical trials have shown that CLA can lead to some reduction in body fat both in normal weight and overweight people, after anywhere from 4 to 12 weeks of supplementation. Study doses ranged from two to four grams of CLA daily. On the flipside, other studies found no beneficial body fat changes at all with supplementation. Some studies showing a beneficial effect from CLA supplementation have also included a calorie restricted diet in the study design. Weight loss result may not always be very impressive.
In one study, subjects lost only 2 to 4 lb. of weight per year, an amount of weight loss that could be achieved with consistent training and sensible dietary adjustments in one month.While these human results are not overly impressive, one recent animal study has raised some concerns regarding the side effects of CLA supplementation. This study found that CLA caused mice to accumulate excessive amounts of fat in their livers. Some animal studies have also found that CLA may raise insulin levels.
The Current CLA Bottom Line
For now CLA supplements are not recommended due to conflicting study results in humans and possible side effects. As far as food sources are concerned, don’t increase intake of fatty animal foods to obtain more CLA. But you can consume more grass-fed beef which increases CLA intake without adding more saturated fat.