The Effects of Dietary Macronutrient Balance on Skin Structure in Aging Male and Female Mice

<div><p>Nutrition influences skin structure; however, a systematic investigation into how energy and macronutrients (protein, carbohydrate and fat) affects the skin has yet to be conducted. We evaluated the associations between macronutrients, energy intake and skin structure in mice fed 25 experimental diets and a control diet for 15 months using the Geometric Framework, a novel method of nutritional analysis. Skin structure was associated with the ratio of dietary macronutrients eaten, not energy intake, and the nature of the effect differed between the sexes. In males, skin structure was primarily associated with protein intake, whereas in females carbohydrate intake was the primary correlate. In both sexes, the dermis and subcutaneous fat thicknesses were inversely proportional. Subcutaneous fat thickness varied positively with fat intake, due to enlarged adipocytes rather than increased adipocyte number. We therefore demonstrated clear interactions between skin structure and macronutrient intakes, with the associations being sex-specific and dependent on dietary macronutrient balance.</p></div

The association between protein intake and male and female skin structure.

<p>H&E staining for male mouse skin layers (a-c) and female mouse skin layers (d-f), x20 magnification, scale bar = 200 μm, ‘d’ indicates area of dermis and ‘s’ indicates area of subcutaneous fat. High protein intake significantly increases male dermis thickness and thins the subcutaneous fat. In females, no effect of protein intake on skin structure was identified. Dietary composition of standard chow is protein (21%), carbohydrate (63%) and fat (16%). Mean skin thickness (a) d = 391 μm, s = 54 μm, (b) d = 275 μm s = 90 μm, (c) d = 228 μm, s = 171 μm, (d) d = 203 μm, s = 148 μm, (e) d = 127 μm, s = 233 μm, (f) d = 194 μm, s = 173 μm.</p

Macronutrient intake influences subcutaneous fat.

<p>Response surfaces showing the association of macronutrient intake (protein, carbohydrate and fat in kJ/d) on subcutaneous adipocyte size (μm²) and adipocyte numbers (cells/10⁵μm²). (a-c) male adipocytes become grossly enlarged with high fat intake whist adipocytes proliferate with high protein intake (d-f; cells/10⁵μm²). (g-i) female adipocytes enlarge to a lesser extent than male adipocytes with high carbohydrate or fat intake and proliferate with increasing protein intake (j-i). For each 2D slice, the third factor is at its median. The red line indicates the ratio of macronutrients that minimizes each response. (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166175#pone.0166175.s005" target="_blank">S4 Table</a>)</p

Dermis thickness (μm) and subcutaneous fat thickness (μm) are inversely proportional and correlate with body fat%.

<p>Dermis thickness increases with a thinner subcutaneous fat in both (a) males (R² = -0.448; P<0.001) then (b) females (R² = -0.362; P<0.001). Subcutaneous fat increases with increasing body fat % in (c) male and (d) female mice (R² = 0.549; P<0.001 and R² = 0.626; P<0.001, respectively).</p

Subcutaneous adipocytes.

<p>Representative H&E sections of mouse subcutaneous adipocytes at 40x magnification showing (a) small male adipocytes become greatly engorged with a high fat intake (b). Small female adipocyte (c) become engorged (d) but to a lesser extent than male adipocytes with a high fat diet. scale bar = 100 μm (See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166175#pone.0166175.s005" target="_blank">S4 Table</a>).</p