Conjugated Linoleic Acid for Weight Control

Some dieters say that CLA helps decrease appetite.

Research suggests that conjugated linoleic acid (CLA) may help to reduce body fat and increase muscle. The research supporting CLA’s ability to help reduce body fat is good, but more is needed. There are at least seven human studies (two are double-blind and the others are controlled) showing significant reduction of abdominal obesity and body fat mass in overweight and moderately obese people. However, since most of the studies involved a small number of participants and were short in duration, larger double-blind studies are needed to further document the benefits and mechanisms of action.

Although CLA promotes weight loss, which is good for heart health, it is important to moniter cholesterol levels as it may reduce HDL (“good”) cholesterol.

A double-blind trial found that exercising individuals taking 1,800 mg per day of CLA lost more body fat after 12 weeks than a similar group taking a placebo.¹ However, two other studies found that amounts of CLA from 0.7 to 3.0 grams per day did not affect body composition.^{2, 3} Most double-blind trials have found that larger amounts of CLA, 3.4 to 4.2 grams per day, does reduce body fat;^{4, 5, 6} however, one double-blind study of experienced strength-training athletes reported no effect of 6 grams per day of CLA on body fat, muscle mass, or strength improvement.⁷

Overweight volunteers who took 4.5 grams of CLA per day for one year had an increase in their blood levels of lipoprotein(a), a risk factor for heart disease.⁸ In a double-blind study of human volunteers, supplementation with 4.2 grams per day of a mixture of cis-9,trans-11 CLA and trans-10,cis-12 CLA for three months increased the concentration of C-reactive protein, another risk factor for heart disease.⁹ In a study of healthy volunteers, supplementing with 4.5 grams of CLA per day for 12 weeks caused an impairment of blood vessel function (endothelial dysfunction), which is believed to be associated with an increased risk of heart disease.¹⁰ Taken together, these findings suggest that long-term use of CLA could increase the risk of developing heart disease.

In a double-blind study of people with type 2 diabetes, supplementing with 3 grams of CLA per day for eight weeks significantly increased blood glucose levels by 6.3% and decreased insulin sensitivity.¹¹ A reduction in insulin sensitivity was also seen in a study of overweight men without diabetes after treatment with 3 grams of CLA per day for three months.¹² However, in another study of obese men and women, supplementation with 6 grams of CLA per day for 24 weeks had no significant effect on blood glucose levels or insulin sensitivity.¹³ Moreover, in a study of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin sensitivity.¹⁴ Although the studies are conflicting, it would be prudent for people who have, or are at risk of developing, diabetes to monitor their blood sugar levels during long-term use of CLA. One unpublished human trial reported isolated cases of gastrointestinal upset.¹⁵

CLA is found mainly in dairy products and also in beef and poultry, eggs, and corn oil. Bacteria that live in the intestine of humans can produce CLA from linoleic acid, but supplementation of a rich source of linoleic acid did not produce increases in blood levels of CLA in one human study.¹⁶ CLA is available as a supplement.