Cycling Nutrition with Monique Ryan: Rapid weight loss and your immune system

Dear Monique:

I have read your column in VeloNews for a while and have both enjoyed and appreciated the knowledge. I have a questions about weight loss and it’s effect on the immune system. For the past few years I have been competing in the sport of triathlon. This year I decided to race bikes for the first six months. I knew that because of the importance of the power to weight ratio, I would need to lose both “after season” weight from last year and some additional body fat to be competitive in the climbs. I set out to lose most of the weight (was 180 lb.) during the first 12 weeks. I wrote down everything that I ate so that my caloric intake was almost always lower than the expenditure by at least 500 calories (more on the five hour ride days). I tried to eat balanced meals and smart snacks. I never had a workout where I felt carb-depleted. My question is, I caught a cold earlier this winter and had some symptoms for over three weeks. When I first felt sick I weighed about 163 lb. or so, but my scale (set-up correctly) said that I was still 16.5-percent body fat. Is there evidence that weight loss affects the immune system? I know that the workouts I was doing could, but in your opinion is there a synergistic effect?
Thanks,
JB

Dear JB,
As you clearly understand, your immune system is affected by a number of factors related to training, nutrition, and lifestyle. More specifically you want to know if weight loss is a separate risk for compromising your immune system. It is a good question, as many cyclists focus on body composition changes and weight loss at this time of year. It appears that you achieved a weight loss of 17 lbs. in about a twelve-week period, which is more than one pound weekly. This is considered a fairly rapid weight loss rate during a cycle of training in which you are completing long distance workouts, such as the five-hour bike rides that you mentioned. In addition, it appears that some of your weight loss could possible have been loss of muscle tissue, if your body fat levels did not lower to the level that you had expected.

There is limited data on the effect of rapid weight loss in athletes, though this has been studied in overweight women.  “In these non-athletes we found that with a weight loss of 1.5 weekly, which was a deficit of 750 calories daily, there was a decrease in T-cell function,” said David Nieman, Ph.D, researcher at Appalachian State University.

Because of this negative effect on the immune system, it is recommended that cyclist lose weight at a rate of one-half to no more than one pound weekly. A drop-off in training from due to illness may not be worth the accelerated weightloss effort. In addition to the calorie restriction that this rate of weight loss represents, it may also represent other nutritional inadequacies. Virtually all nutrients in our diet play some sort of role in keeping our immune system healthy.

“Our immune system is heavily dependent on glucose and the amino acid glutamine,” said Dr. Nieman. “When the carbohydrate and amino acid supply is down our immune system can be compromised. ”Even if you paid attention to consuming carbohydrate during hard workouts, particularly those long training rides, you may not have been consuming enough for adequate recovery because of your accelerated weight loss efforts. By cutting back at least 500 calories daily, it is assumed that some of these calories came from carbohydrate and protein sources, which could have compromised your daily glycogen repletion and recovery from one training session to the next.

Several studies have looked at the impact of dietary carbohydrate on hormonal and immune response to exercise. When exerciseis completed over several days time on a low carbohydrate diet the magnitude to which stress hormones respond to exercise is much higher than with adiet adequate in carbohydrate. While these experimental diets were very low in carbohydrate, it is assumed that athletes who are carbohydrate deficient in their daily diet are placing themselves at risk from the known immunosuppressive effects of hormones such as cortisol.

Keep in mind that the amount of carbohydrate that you require on a daily basis is related to the duration and intensity of your training sessions. In addition to your carbohydrate status, your dieting could also have compromised your protein status, particularly if your weight loss efforts resulted in the loss of lean body mass. It is good that you brought up the point of not completing workouts in a carbohydrate depleted state, at it may help other cyclists appreciate the risks of not replacing carbohydrates during training.

While your muscleglycogen stores may not have been optimal at the start of certain training sessions, I am assuming that you are referring to your carbohydrate intakeduring training. Because much of the immune function impairment related to exercise is mainly from an elevated concentration of stress hormones, one of the nutritional strategies that could effectively reduce this stress hormone response to exercise is the effect of carbohydrate consumption during training. Several studies indicate that consuming carbohydrate during exercise does a better job of maintaining blood glucose levels during exercise, and that this weakens the usual rise in stress hormones such as cortisol, results in less dysfunction of the immune system, and in less inflammation.

“We are now analyzing data in which cyclists trained for three hours at 65- to 67-percent VO₂ max, and comparing carbohydrate intake during this exercise to a placebo. What we have found is that parts of the immune system show less dysfunction and less inflammation with the carbohydrate consumption,” said Dr. Nieman.

“We still need to determine if this translates into less infection.”

When you are on a calorie restricted diet in an attempt to lose weight, you can also compromise your vitamin and mineral intake. Though true deficiencies are not common, insufficient intake could affect your resistance to infection. So, it is best to eat a balanced diet of high quality foods to keep vitamin and mineral stores in the body at optimal levels. If you do supplement, keep to modest doses, as excesses of some minerals such as iron and zinc can impair immune function and increase your susceptibility to infection.

For cyclists trying to improve their strength to weight ratio, it is best to approach any type of weight loss, or body fat loss slowly. This prevents nutrient deficiencies and should keep your immune system stronger.

Good luck,

Monique

Monique Ryan, MS, RD, LDN

is a nationally recognized nutritionist with over twenty-two years of experience and is owner of Personal Nutrition Designs, a Chicago based nutrition consulting company that provides nutrition programs for endurance athletes across North America. Monique consults with the Chicago Fire Soccer Team, and was the nutritionist for Saturn Cycling from 1994 to 2000. She has also consulted with the Volvo-Cannondale Mountain Bike Team, the Gary Fisher Mountain Bike Team, and the Rollerblade Racing Team. Monique has consulted with USA Cycling, and was a member of the Performance Enhancement Team for the Women’s Road Team leading to the 2004 Athens Olympics. She has also provided nutrition consultation services to USA Triathlon for coaching clinics, athlete clinics, and for the resident athlete team and was a member of the USAT Performance Enhancement Team for the 2004 Athens Olympics. Monique is the author of “SportsNutrition for Endurance Athletes,” 2nd edition (March 2007), from VeloPress,which provides sports specific nutrition for road cycling, mountain biking, running, triathlon, swimming, rowing, and adventure racing. She is also author of “PerformanceNutrition for Winter Sports” (PeakSports Press), “Performance Nutritionfor Team Sports” (PeakSports Press), and “Complete Guide to Sports Nutrition. Monique is a regular contributor to VeloNews, Inside Triathlon, Outside, and ACE Fitness Matters. Please send your questions to velonewssteve@competitorgroup.com.

FILED UNDER: Coaches Panel / Nutrition TAGS: feedzone / Monique Ryan / Training / weight loss