Isoenergetic Feeding of Low Carbohydrate-High Fat Diets Does Not Increase Brown Adipose Tissue Thermogenic Capacity in Rats

Low-carbohydrate, high-fat (LC-HF) diets are popular for inducing weight loss in overweighed adults. Adaptive thermogenesis increased by specific effects of macronutrients on energy expenditure has been postulated to induce this weight loss. We studied brown adipose tissue (BAT) morphology and function following exposure to different LC-HF diets

Weight curves of rats on the control diet (circles, fed ad libitum), compared to the three experimental diets (iso-energetic pair feeding): low-carbohydrate high-fat, low-protein diet (LC-HF-LP; squares), low-carbohydrate high-fat, normal-protein diet (LC-HF-NP; upward triangles) or high fat diet (downward triangles); p<0.0005, repeated measurements ANOVA.

<p>The cumulative average weight gain for each group during the four week feeding period is given in the insert, analyzed by global one-way ANOVA and Dunnett tests for pairwise comparison vs. control: * p<0.05, *** p<0.001. Data are shown as means±SEM; n = 7 animals/group.</p

Weight of interscapular brown adipose tissue (iBAT) in rats fed control or experimental diets (LC-HF-LP, LC-HF-NP, high fat).

<p>A: total weight (absolute); B: percentage of body weight (relative). Data are shown as means±SEM, n = 7/group; analyzed by global one-way ANOVA and Dunnett tests for pairwise comparison vs. control. * p<0.05, ** p<0.01 vs. control.</p

In-vivo measurement of maximal adaptive thermogenic capacity in rats fed the control or experimental diets (LC-HF-LP, LC-HF-NP, high fat).

<p>A: respiratory quotient after feeding control or experimental diets for 4 weeks: basal and following norepinephrine injection. B: Basal and norepinephrine stimulated energy expenditure (EE), expressed as kcal/h/kg BW^0.75. The time points 0 min and 36 min are not given, as cages had to be opened for animal handling and measures of RQ and EE are not reliable at these time points. The insert shows the mean EE of timepoints 77, 84 and 91 min. Data are shown as means±SEM; n = 7 (control), 6 (LC-HF-LP), 5 (LC-HF-NP), 7 (high fat). Statistical analysis was performed on the average of three time points at baseline and during the plateau phase after NE injection, respectively, using global one-way ANOVA and Dunnett tests for pairwise comparison vs. control.</p

Body core temperature in rats fed control or experimental diets (LC-HF-LP, LC-HF-NP, high fat).

<p>A: morning, B: evening. Data are shown as means±SEM; n = 7/group; analyzed by global one-way ANOVA and by Dunnett tests for pairwise comparison vs. control.</p

Primer sequences (5′-3′).

<p>Primer sequences (5′-3′).</p

Quantitative real time PCR in iBAT following control or experimental diets (LC-HF-LP, LC-HF-NP, high fat).

<p>ADRB3: β3 adrenergic receptor. Gene expression was normalized to 18 S rRNA. Data are shown as means±SEM; n = 7/group; analyzed by global one-way ANOVA and by Dunnett tests for pairwise comparison vs. control. * p<0.05, ** p<0.01 vs. control.</p

Respirometry.

<p>Measurement of mitochondrial oxygen consumption using microplate based extracellular flux analyzer in tissues from rats fed the control or experimental diets (LC-HF-LP, LC-HF-NP). A: brown adipocyte mitochondria. B: muscle mitochondria. Stage II, basal; stage III, ADP; stage IVo, oligomycin. N = 3/group.</p