May 31, 2018
People who avoid animal fat could experience slower muscle growth when they exercise because of choline deficiency, new research shows.
"Less than the ideal amount of choline intake may be impairing your strength gain," said Chang Woock Lee, PhD, from the School of Education, Health Professions and Human Development at the University of Houston–Victoria.
However, consuming more than the recommended amount of choline did not produce additional benefits, he said here at the American College of Sports Medicine 2018 Annual Meeting.
Choline plays an essential role in cell membrane integrity, lipid transport, and methylation. It is a precursor to acetylcholine, the neurotransmitter in motor neurons that mediates muscle contraction.
In previous studies of cholesterol, Lee and his colleagues noticed an association between the amount of cholesterol consumed and the ability to gain strength. That got the researchers interested in the micronutrients found in the same foods as cholesterol. Of these, choline emerged as the most important.
To see how choline affects muscle responses to resistance training, the team supplemented the diets of 37 people, 50 to 69 years of age, with different amounts of choline. The 13 people assigned to the low group received 0.7 mg of choline per kilogram of lean dietary mass, the 11 people assigned to the medium group received 2.8 mg/kg, and the 13 people assigned to the high group received 7.5 mg/kg.
The diet consumed and carefully documented by the participants was 50% carbohydrates, 20% protein, and 30% fat (less than 10% of which was saturated). Choline was consumed in the form of supplemental egg yolk, and all participants supplemented their diets with 0.8 g of protein per kilogram of lean dietary mass.
There were no significant differences in age, sex, height, weight, body fat, lean body mass, or body mass index among the three groups. Nor were there significant differences in the consumption of total energy; energy from carbohydrates, protein, or fat; percent of kilocalories from carbohydrates, protein, or fat; folate; vitamins A, B5, B6, B12, C, D, or E; or betaine.
The high-choline group consumed significantly more cholesterol, but choline was independently associated with increased strength, Lee reported.
Three times a week, the participants performed eight exercises in three sets of eight to 12 repetitions at 70% of 1 maximum repetition.
The consumption of choline was estimated to be 6.2 mg/kg of lean dietary mass in the low group, 8.1 mg/kg in the medium group, and 14.2 mg/kg in the high group.
The amount of choline consumed in the high group was more than the adequate intake recommended by the Institute of Medicine Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its panel on folate, other B vitamins, and choline, which suggests 550 mg/day for men and 425 mg/day for women, with a tolerable upper intake level for adults of 3.5 g/day.
After 12 weeks of diet and exercise, Lee and his colleagues measured participant strength as a composite of 1 maximum repetition bench press and 1 maximum leg extension.
On average, composite strength was lower in the low group than in the medium and high groups (29.4% vs 46.8% vs 47.4%). The difference between the low and medium groups was significant (P = .034).
And improvement in thigh muscle quality — measured by 1 maximum repetition leg press — was significantly less in the low group than in the medium and high groups (12.3% vs 46.4% vs 46.4%; P = .01).
This finding is "fascinating," said Samantha Leyh, MS, RD, from the Air Force Research Laboratory in Patterson, Ohio. "I'm very surprised that supplementing with choline would have that big an effect."
Low choline consumption might be common among older adults because the usual sources often contain animal fat and cholesterol, which people seeking a healthy diet often avoid, Lee explained.
"People are afraid of egg yolk," he told Medscape Medical News.
Research has shown no ill effects from dietary cholesterol, he said, adding one caveat: cholesterol could harm people who are not exercising enough because it can build up in the bloodstream instead of being incorporated into growing cells.
Optimum choline intake could depend on exercise, as well, he pointed out.
It is hard to get adequate amounts of choline from plant foods, although it is present in, for example, soy beans. Some research has shown that supplements containing phosphatidylcholine are more bioavailable than supplements containing choline chloride or choline bitartrate, Lee said.
The study was funded by the US Poultry and Egg Association. Lee and Leyh have disclosed no relevant financial relationships.