Low-protein and methionine, high-starch diets increase energy intake and expenditure, increase FGF21, decrease IGF-1,...

Area of Science:

• Nutrition Science
• Metabolic Regulation
• Animal Models

Background:

• Low-protein diets often lead to increased energy intake to meet protein requirements, posing a risk of fat accumulation.
• Dietary protein quality, particularly methionine content, can influence metabolic responses to protein restriction.

Purpose of the Study:

• To investigate the effects of reduced dietary protein content and quality on energy intake, body composition, and metabolic markers in mice.
• To explore the role of fibroblast growth factor 21 (FGF21) in mediating responses to low-protein diets.

Main Methods:

• Female BALB/c mice were fed diets with varying casein or soy protein levels (20%, 6%, 3%).
• Measurements included energy intake, body composition, energy expenditure, glucose tolerance, insulin response, and tissue/plasma levels of key metabolic factors (FGF21, IGF-1, etc.).

Main Results:

• Reduced protein intake increased energy intake and slightly increased adiposity, but total energy expenditure rose proportionally, limiting fat gain.
• Lean body mass was preserved at 6% protein but reduced at 3% casein. Insulin response was blunted in soy- and low-protein-fed mice.
• Plasma FGF21 levels increased with protein restriction and were influenced by protein level, protein-to-carbohydrate, and protein-to-methionine ratios. FGF21 was also elevated in brown adipose tissue and liver.

Conclusions:

• Decreased dietary protein and compromised protein quality increase energy intake and expenditure, resulting in only minor increases in adiposity.
• FGF21 is a significant signaling molecule that responds to dietary protein restriction, protein quality, and carbohydrate content.