LINOLEIC ACID (CLA)
Linoleic acid is found in the diet in vegetable oils, whereas the conjugated variety, CIA, is found primarily in meat and dairy products. The form of CLA found most commonly in dietary supplements is manufactured from vegetable oils, such as sunflower oil. It is marketed primarily as a weight loss and muscle-building supplement and also as an “anticancer” agent.
Linoleic acid is an co-6 fatty acid, meaning that it is unsaturated, with a double bond occurring at the sixth carbon atom. CLA is an isomer of linoleic acid, which refers to a slight rearrangement of the molecular structure (conjugation) resulting in a fatty acid with altered chemical functions. The rearrangement in this case is a conjugated double bond occurring at carbons 10 and 12 or at carbons 9 and 11; this may be an important distinction because a number of recent studies have suggested that the two isomers may have different metabolic fates in the body.
The existing evidence supports a beneficial, but modest, effect of CLA supplements (3-6 g/dayfor4-12 weeks) in promoting fat loss in moderately overweight adults. Athletes do not appear to derive the same weight loss or lean-mass-enhancing effects that have been observed in studies of overweight sedentary subjects. Anticancer claims for CLA supplements are based on preliminary laboratory findings and are not supported by convincing clinical evidence.
Most research on the dietary intake of CLA has been conducted in animals. Weight loss studies in rodents have shown a beneficial effect of CLA feeding, with supplemented rats gaining less body fat but more lean body mass compared with control animals. In livestock studies (cattle, pigs, and chickens), supplemental CLA has been shown to promote growth and prevent muscle wasting, whereas body fat accumulation may be suppressed owing to an increase in energy expenditure. In rabbits with high cholesterol, CLA feeding reduces LDL and triglycerides.
In humans, Noone et al. (2002) showed that blended CLA supplements (3 g of either a 50:50 or 80:20 blend of c9/tll:tlO/c!2) could reduce fasting plasma triglyceride and cholesterol levels but with no effect on levels of HDL, glucose, or insulin or on body weight in healthy normolipidemic subjects. A similar study by Benito et al. (200la) found no change in blood levels of cholesterol or triglycerides in normolipidemic subjects consuming 3.9 g/day of CLA for 93 days.
GUARANA (PAULLINIA CUPANA)
Guarana is a Brazilian herb that may be found in supplements and foods (because it is generally recognized as safe). It has become a popular addition to energy drinks owing to its high caffeine content. Traditionally, guarana has been used as a mental, physical, and sexual stimulant. Today, guarana is mostly used for energy, for athletic performance, and in weight loss formulations, but preclinical studies are exploring its effects on increasing sexual function.
No clinical work has been performed on guarana as a single ingredient, so its use as a supplement relies on its traditional medicinal use and the strength of the research behind caffeine for inducing alertness, suppressing the appetite, and promoting thermogenesis. Although caffeine is accepted as the major active ingredient, other important compounds in guarana are under ongoing investigation, including polyphenols and saponins (Henman, 1982).
No clinical studies have been performed with guarana as a single supplement in humans; therefore, even though there is much clinical support for the use of caffeine on the claims of mental and physical performance, claims for the use of guarana as a whole herb remain largely unfounded.
Although guarana has been tested in studies of weight loss, it is formulated with other herbs, so these studies were not included in this review (Andersen and Fogh, 2001; Bouthegourd et al., 2002). Guarana is sometimes formulated with ephedra or supplements containing ephedrine alkaloids to trigger the well-known and studied synergistic effect between caffeine and ephedrine alkaloids (Nasser et al., 1999). Boozer et al. (2001) found that ephedra (ma huang) and guarana produced fat and weight loss. Another study of the impact on obesity of a formulation containing several herbs, including guarana, found favorable results on weight loss. The formulation contained the standardized ingredients of ephedra, caffeine, and chromium picolinate from the herbal mixture (Woodgate and Conquer, 2001).
The use of guarana for athletic performance has been tested in mice on measures of exercise-induced hypoglycemia and in physical and cognitive tests with favorable results. Additionally, a mixture of herbs including guarana was found to relax rabbit corpus cavernosum (Antunes et al., 2001; Espinola et al., 1997).
The dosage of guarana is from 200-2,000 mg/day, in divided doses, of an extract standardized to 5.5-10% of caffeine (providing 11-200 mg of caffeine per serving). A dosage of more than 200 mg of caffeine per serving (in supplement, food, or beverage) is not recommended.
The safety concerns of guarana are mainly owing to the caffeine content. Persons who are caffeine sensitive may be overstimulated at higher doses, with possible symptoms of related insomnia, restlessness, anxiety, high blood pressure, irritability, headaches, and heart palpitations. Guarana is not recommended for pregnant women or children. The American Herbal Products Association (AHPA) has given guarana a Class 2 rating: “not recommended for excessive or long term use” (McGuffin et al 1997).
Another concern for guarana toxicity is for formulations containing ephedra (ephedrine alkaloids). Consumption of ephedrine alkaloids and caffeine have well-known and serious cardiovascular risks.