Interesting Animal Study

Came across an interesting study on the Nutrition and Metabolism Society website that offers yet more support for restricting carbohydrate intake when trying to lose weight and or build muscle. You can find the complete study here.

While studies in rats do not necessarily mean that the same principles will hold true exactly in other animals, such as humans, it does give some food for thought.

Basically the study compared to groups of normal adult male rats were fed either a high carb/low protein diet or a high protein/moderate carb diet (could be low carb depending on your definition I suppose.
Adult, male rats were fed either a high carbohydrate (CHO) diet (60% of energy from carbohydrates, 12% protein, 28% fat; n = 30) or a high protein (PRO) diet (35% carbohydrate, 35% protein, 30% fat; n = 30).

While I understand some of the technical discussion, much of it is over my head at this point as I'm not familiar with all the terms yet. The part I understand is that the two diets caused different forms of GLUT4 release after eating. GLUT4 is a protein that transports glucose into either muscle or fat cells, and is only found in those types of cells. According to Wikipedia:

At the cell surface, GLUT4 permits the facilitated diffusion of circulating glucose down its concentration gradient into muscle and fat cells.

 The high protein diet caused a higher release of GLUT4 in muscle cells at lower insulin levels, reflecting better insulin sensitivity. This would tend to cause more glucose to be transported into the muscle cells to be used for energy rather than to the fat cells for storage. The reverse happens with the high carb diet, which produces much higher insulin levels and a preference to store extra glucose in the fat cells. The report says this is consistent with other findings and suggests "that animals chronically consuming a CHO diet will preferentially rely on adipose to dispose of excess glucose after a high carbohydrate meal."

Two other biological markers are mentioned.

One set ERK1/2, which when elevated is usually a marker of cell division and growth is much higher in both fat and muscle tissue (more so in fat) after a high carb meal. With a protein meal there is some rise in the level of this marker in muscle cells but a marked decrease in fat cells. Taken together with the GLUT4 levels mentioned above it means that with a high carb meal, fat cells tend to get more of the glucose from the meal and the fat cells may have a tendency to grow and divide, allowing for even more storage.

The other marker mentioned is p70S6k, which generally indicates greater protein turnover in muscle cells and greater energy production. A carb meal has little or no impact on this marker while a protein meal, not surprisingly, increases it dramatically.

The authors conclude:

Animals chronically consuming the CHO diet produced greater metabolic signaling in adipose tissue to handle excess glucose and blunted signaling in skeletal muscle consistent with interpretation of insulin resistance. Conversely, animals consuming the PRO diet produced greater metabolic signaling in skeletal muscle with little signaling in adipose. While these data suggest that consuming an increased CHO:PRO diet may have detrimental effects on insulin sensitivity, the long-term significance of these metabolic differences warrants further investigation.