Creatine, Conjugated Linoleic Acid, and Resistance Training
By Dónal P. O'Mathúna, PhD. Dr. O'MathÚna is a lecturer in Health Care Ethics, School of Nursing, Dublin City University, Ireland; he reports no financial relationships relevant to this field of study.
With the recognition that exercise must be part of any weight loss program, some attention has been given to the optimal role of dietary supplements. One suggestion has been that certain supplements may support the beneficial changes in body composition that accompany resistance exercise. People who are overweight will benefit not only from losing weight, but also from reducing the proportion of fat in their bodies and increasing their fat-free mass (FFM). Exercise can use up some of the fat stored in the body and increase muscle mass and strength. This has led to interest in whether certain supplements stimulate similar changes in body composition. The combined administration of two such supplements, creatine and conjugated linoleic acid (CLA), along with resistance training, recently produced intriguing results among older adults.1
Creatine has been a very popular supplement among athletes.2 Much evidence supports claims that creatine enhances power output during short maximal bursts of exercise, such as power lifting or sprinting.3 The benefit is noted particularly when the bursts are repeated intermittently in what is called interval training. These outcomes have led to interest in using creatine to promote development of muscle and FFM. Aging is associated with reduced muscle mass and strength, which can lead to functional impairment and reduced quality of life. Sarcopenia refers to the condition when fat free mass is more than 2 standard deviations below normal.1 Resistance training is also suggested for age- and disease-related loss of muscle mass, strength, and function.4 Numerous studies have demonstrated that resistance exercise counteracts sarcopenia, leading to investigation of complementary strategies to supplement those gains. Exercise with supplementation might be preferable to exercise alone or other invasive or pharmacological alternatives.
CLA has received less research than creatine as a dietary supplement. Interest in CLA developed after a number of animal studies showed a reduction in body fat when the animals consumed CLA, regardless of their quantity or type of fat intake.5 This has led to some research into its use as a supplement that might generate favorable changes in body composition in humans.
Creatine is made from three amino acids common to protein. On average, people require about 2 g of creatine daily, obtained equally from exogenous and endogenous sources.6 Humans store 95% of their creatine in skeletal muscle, with more found in fast twitch muscle fibers than slow twitch ones.7 Creatine is essential to allow regeneration of muscles' biochemical energy levels so that intense exercise can be sustained.
CLA is a group of very closely related natural chemicals belonging to the omega-6 fatty acids.5 Supplements usually contain a mixture of these fatty acids, although two tend to predominate. CLA occurs naturally in dairy products, beef fat, and some plant oils.1 However, the amount of CLA in milk, for example, varies enormously depending on the cows' diet (grazing or feed) and time of the year (highest when cows graze on rapidly growing grass).5 Such background variability complicates attempts to study the impact of CLA on body composition. Studies of creatine and CLA combinations are further complicated by large variability found in individual responses to creatine supplementation.
The first study examining creatine and CLA supplementation with resistance training involved 39 community-dwelling, healthy adults (aged 65-85 years).1 Participants were randomized to receive either creatine (5 g/day) with CLA (6 g/day) or placebo for 6 months. No participants had engaged in an exercise program during the previous 2 years, and all participated in supervised resistance training twice a week for the duration of the study. All measures of strength increased for both groups. Isokinetic (resistance at a constant speed) strength increased significantly more in the supplement group (P < 0.05), but isometric (performed at static position) strength gains did not differ between the groups. The supplement group had significantly better increases in FFM and decreases in total fat mass (P < 0.05).
Use of CLA has been promoted on the basis of animal studies showing that CLA supplementation led to reduced weight gain. However, other animal studies have shown no effects from CLA supplements.8 Where effects did occur, they were dependent upon the amount and type of compounds present in the CLA mixture. The results of trials in humans have been inconsistent, with no dose response effect and a smaller effect size than seen with animals. A study with twenty healthy adults, who exercised for 90 minutes three times a week in the gym, found significant reductions in body fat with CLA compared to placebo.9 However, differences in body weight were not found between the two groups. In another study, 17 healthy women (aged 20-41 years) were randomly assigned to receive either CLA or placebo.10 They lived in a controlled metabolic unit for 94 days. No significant differences were found between the groups for changes in body weight, fat mass, FFM, or percentage body fat. Energy expenditure and respiratory parameters did not vary between the groups either at rest or when walking. Similar non-significant results were found for CLA supplementation in experienced resistance-training men (mean age 23 years).11
The use of creatine supplements with resistance training among older, non-athletes dates back from the late 1990s.12 Thirty-two men and women (67-80-years-old) were randomized into four groups: creatine with resistance training, placebo with training, creatine without training, and placebo without training. None of the participants did weight-lifting before the study, and all were sedentary-to-moderately active. Creatine dose was 20 g/day for 5 days, followed by 3 g/day for a total of 8 weeks. Resistance training was carried out 3 times a week. No significant changes in body mass or body fat were found in any group. Training groups had significantly increased strength and endurance compared to those not training. Creatine supplementation did not provide any additional benefit.
A double-blind, randomized trial assigned 30 men (mean age 70 years) to receive either creatine (0.3 g/kg for 5 days, followed by 0.07 g/kg daily) or placebo.13 Both groups engaged in three sessions of resistance training per week for 12 weeks. Both groups had significantly increased FFM, with the increase being significantly greater in the creatine group (P < 0.05). Fat mass did not differ between the two groups. With two of the three muscle groups trained, the creatine group had significantly greater improvements in strength and endurance. The training volume was 31% higher in the creatine group (P = 0.05). Training volume is a measure of the total amount of exercise calculated from the total weight used and the total number of repetitions.
Creatine frequently leads to a weight gain of 1-3 kg, probably due to intramuscular water retention.14 Numerous anecdotal reports from athletes claim creatine supplementation causes gastrointestinal problems, muscle cramping, and renal problems. One study with older men found significantly more reports of loose stools during creatine loading than with placebo.13 Also, after 3-5 weeks, muscle cramping and strains were more frequent with creatine than placebo. Whether creatine adversely affects renal function remains controversial and unclear, suggesting that those at high risk for renal disease should be monitored medically.15
CLA has similarly been reported to cause gastrointestinal problems. However, the impact of CLA on insulin resistance is of more concern. While commentators on the animal studies have focused on CLA's beneficial effects, recorded adverse effects have been largely ignored.8 Numerous animal studies have found that CLA induces insulin resistance and, thus, should be avoided by anyone at risk of diabetes. Animal studies have also found enlargements in the liver and spleen. However, little is known about the actual risks from CLA supplementation in humans.
Creatine is readily available from meat and fish (containing roughly 4-5 g/kg) and, therefore, is classified as a dietary supplement, not a drug. It is most commonly available as a monohydrate in powder, candy, gum, and liquid. Numerous products combine it with vitamins, nutrients, and other supplements. Athletes usually "load" with 20 g creatine per day for 4-6 days (usually 5 g four times daily), followed by 2 g daily. Less is known about the optimal dose of CLA, but 3 g daily is commonly recommended.5
Support for using creatine and CLA, along with exercise, for improved body composition arises primarily from one study. While rigorously designed, such results require replication before use of such a program can be generally recommended. Oral supplementation with creatine alone has been studied extensively in athletes, with much less research in healthy non-athletes. Where resistance training has shown itself to be beneficial, some evidence supports the addition of creatine supplements. However, the early stage of this research must be noted, especially given the potential for complications in the elderly, especially those with co-morbidity. The evidence base to support CLA supplementation along with exercise is even smaller. Support comes primarily from animal studies, but these also reveal concerns about adverse effects. Much further research is needed into CLA before its use as a supplement should be promoted.
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