17 years ago as a newbie Physical Therapist, I had the distinct pleasure of working with my first centenarian. We talked about many things during his rehabilitation, but my favorite was his simple response to my question of "What is the secret to living 100 years?" This man was a Jewish Rabbi, father, grandfather and a successful businessman during his working years. Surely many things could have entered the conversation here. His answer? "I always kept the kettle boiling." Translation - he never ate to his full capacity. When a tea pot is full, there is no room for it to boil and whistle. Instead, the water sputters out and that full boil is never achieved. Think about it. So simple, but such sage advice. And, I have never forgotten it.
Recently, I read an article about how endurance training reduces insulin secretion. (Insulin is your body's hormonal response to sugar in the blood stream. Its job is to help the cells take in and use the blood sugar and return your body to homeostasis after you ingest a starchy or sugary food.) As a self-proclaimed amateur endurance athlete, I was interested in the notion that my training would decrease my body's secretion of insulin both at rest and during exercise. How would it do this? And, how will that effect the aging process?
Really, the body is an amazing machine. The carbohydrates we eat act as the source of fuel for both the skeletal muscle and the heart and brain of the endurance athlete. The notion of carbo-loading has been touted to help build the stores of carbohydrate in the body tissue. On average, we are only able to store 10-20 calories of carbohydrate per pound of body weight. When we start exercising, the carbohydrate stored in the liver and skeletal muscle (now called glycogen) is broken down to maintain blood sugar levels and provide energy for exercise performance. Carbohydrate ingestion 3 days before an event will supply the muscles with adequate fuel, and breakfast before the race will ensure the mental stamina. Additional intake of 30-60 g/hour during exercise has also been advised to delay the onset of fatigue in trained athletes (Gu, Clif shots, gummy bears and gatorade all apply here).
Taking all of this into account, it is the process of insulin sensitization, achieved by 1. aerobic exercise, 2. low fat/high carbohydrate diet and 3. loss of body fat, that allows for the reduced insulin secretion. If your body is more sensitive to the insulin it produces, it need not produce more. (Conversely, insulin in-sensitivity is a precursor to diabetes. The insulin is there, but the cells are not receptive to it and so the body secretes more, trying to restore the blood sugar-insulin balance.) Each of the three components are a natural part of endurance training. Ah-ha! Mystery solved.
Now, how about the aging effect? Well, it's like the wise man said. Keep the kettle boiling. Science continues to point to calorie-restriction as an effective route toward longevity. The longest-lived humans and animals share the following traits: low fasting glucose, low percent body fat, low triglycerides, low body temperature and... low fasting insulin levels.
Food for thought?
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