Muscle, Diet and Exercise

[Guest guest]

The following article should be of interest to those of you who read the

recent discussions that we have been enjoying on nutrition, strength training

and diabetes.

http://www.afpafitness.com/articles/MuscleExercise.htm

Muscle, Diet and Exercise : Recent Research Findings

[Excerpts given ...]

Skeletal muscle is a major player in whole body energy balance, lipid-based

energy flux and insulin-stimulated glucose uptake. Dr Storlien's research on

metabolic syndromes such as diabetes has shown that the specific fatty acid

composition of the major structural lipids in the sarcolemmal membrane

significantly influences membrane morphology and behavior and, in turn,

certain aspects of cellular and whole body metabolism and physiology.

It appears that both the degree of unsaturation, and the omega-6:omega-3

ratio influences membrane, cellular, and ultimately whole body function. For

example, the higher the level of membrane unsaturation, the higher the

insulin sensitivity. A diet with a low polyunsaturated:saturated fat ratio is

believed to be a causal factor in hyperinsulinemia. A higher unsaturation

ratio increases GLUT 4 activity, which is important for glucose transport

into the muscle during exercise. Omega-3 (n-3) polyunsaturated fatty acids,

found in foods from marine origin and in a few seed oils (e.g. canola), may

also play a particularly important role in insulin action.

A high n-6:n-3 ratio, typical of a modern western diet containing high levels

of vegetable oil, appears deleterious and is related to an increased

incidence of some cancers, behavioral problems, a dysfunctional immune system

and cardiovascular disease (Okuyama et al., Prog. Lipid Res. 35, 409-457,

1997). Insulin action also appears to be influenced by the activity of the

delta-5-desaturase enzyme, which is involved in the competitive conversion of

essential n-6 and n-3 fatty acids to their membrane storage forms. The

activity of delta-5-desaturase enzyme has been shown to be increased by high

protein diets, glucose, and insulin, and depressed by glucagon, epinephrine,

cAMP, and fasting.

With relevance to obesity research, Dr Storlien explained that the lower the

n-6:n-3 ratio, the greater the membrane fluidity, the greater the proton

leakage from the cell, and consequently the greater the cellular metabolic

rate. On the other hand, high rates of proton leakage may be detrimental to

exercise performance by increasing the amount of energy required to fuel

active ion transporters responsible for ionic and acid-base homeostasis.

Helge et al. (J. Physiol. 491, 63P, 1996) recently reported that endurance

time tended to be greater in trained rats consuming a high saturated fat

diet, than in rats on a high unsaturated fat and high carbohydrate diets.

In relation to fiber type, highly oxidative and insulin-sensitive type I and

type IIa fibers appear to possess relatively unsaturated sarcolemmal

membranes, with a greater percentage of n-3 fatty acid integration, compared

to type IIb fibers. Endurance training has only a small effect on increasing

the degree of unsaturation of the membrane. In contrast, dietary fatty acid

content exerts a powerful influence. Training alone does appear to increase

membrane fluidity by decreasing the level of cholesterol.

Studies of Caucasian and Pima Indian populations suggest there is a genetic

factor determining the processing and incorporation of fatty acids into the

sarcolemmal membrane. Pima Indians have high rates of heart disease,

diabetes, obesity, low levels of n-3 membrane fatty acids and

delta-5-desaturase enzyme activity, and a relatively high proportion of type

IIb fibers, all compared to Caucasian populations.

Heavy exercise has been shown to release non-esterified fatty acids directly

from the sarcolemma into plasma, where they become available for uptake and

eventual oxidation. Unsaturated fatty acids were recently suggested to be

more easily oxidized as fuels during exercise. This is based on the

observation of a lower respiratory exchange ratio in a group of rats fed a

high unsaturated fat diet compared to high saturated fat and high

carbohydrate diets (Helge et al, 1996).

Others have argued, on biochemical grounds, that saturated fats, especially

short and medium chain, should be the best fuel for exercise because they do

not require biotransformation before they can be oxidized as fuel. Athletes

and physically active people may benefit from habitually increasing their

intake of dietary unsaturated fatty acids, particularly mono-unsaturates and

polyunsaturated n-3, by increasing membrane fluidity and insulin sensitivity.

Athletes may also benefit from ingesting saturated fatty acids as a

pre-exercise meal and an exercise supplement.

The striking message I took home from Dr Storlien's talk was that diet,

exercise and genetics are likely to interact in complex ways to influence

cellular physiology and whole body responses. And although we still have much

to learn, it seems that science is moving steadily towards optimizing diets

for health and athletic performance. .....>

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Dr Mel C Siff

Denver, USA

http://groups.yahoo.com/group/Supertraining/