Author(s): SKRIVER, S., VIGH LARSEN, J., MOHR, M., HANSEN, M., Institution: AARHUS UNIVERSITY, Country: DENMARK, Abstract-ID: 2402

INTRODUCTION:
Overweight is a global concern, affecting more than half of the Danish population. A calorie restricted diet combined with physical activity is considered optimal for weight loss and improving cardiovascular and metabolic health, including muscle mass maintenance and cellular adaptations. Carbohydrate (CHO)-restricted diets, such as the ketogenic diet, have become increasingly popular for weight loss and metabolic health, but their impact on physical capacity remain unclear. This study investigated how a very low CHO (VLCHO) diet combined with caloric restriction affects weight loss, physical capacity and metabolic parameters.
METHODS:
Forty healthy young women (BMI 25–30 kg·m⁻²) were randomized to 12 days of VLCHO (0.3 g CHO·kg⁻¹·day⁻¹) or a moderate CHO diet (MCHO) (2.5–3.0 g CHO·kg⁻¹·day⁻¹), both with a 1000 kcal·day⁻¹ deficit and 1.4 g protein·kg⁻¹·day⁻¹. Participants completed three supervised bike sessions between baseline (pre) and day 11 (post 1). Body composition, resting metabolic rate (RMR), substrate utilization, blood markers, muscle biopsies, and performance were assessed pre and post 1. Performance was reassessed on day 13 (post 2) following a CHO-rich breakfast.
RESULTS:
VLCHO reduced daily blood glucose and increased ketones compared with MCHO (group × time, P<0.001). Body weight decreased more in VLCHO (–3.3 vs –1.3 kg; group × time, P<0.001). FFM declined in VLCHO (–2.1 kg; P<0.001) but was preserved in MCHO (group × time, P<0.001). Total body water decreased only in VLCHO (group × time, P<0.001). Fat mass decreased similarly between groups, whereas body fat percentage decreased only in MCHO (group × time, P=0.006).
At post 1, time to exhaustion decreased in VLCHO (–52 s; P=0.018) but not in MCHO (group × time, P=0.001). At (post 2), VLCHO returned to baseline, whereas MCHO showed a net improvement from pre (+101 s; P<0.001). Peak sprint power declined in VLCHO at post 1 (–52.8 W; P<0.001) and remained lower at post 2 (net –32.3 W; P=0.017), whereas MCHO increased at post 1 (+30.0 W; P=0.035) with no net change at post 2 (group × time, P<0.001). Average sprint power decreased in VLCHO at post 1 (P=0.009) with no significant net change at post 2.
Peak fat oxidation increased more in VLCHO (group × time, P=0.005) and remained elevated at post 2. Respiratory quotient decreased only in VLCHO (group × time, P=0.010). RMR decreased in MCHO (P=0.008) but not in VLCHO.

CONCLUSION:
VLCHO during short-term energy restriction induced pronounced metabolic adaptations, including ketosis and increased fat oxidation, but at the expense of FFM and high-intensity performance. These impairments were only partially restored after acute CHO refeeding. In contrast, MCHO preserved lean mass and improved endurance capacity. CHO availability critically modulates the balance between metabolic adaptation and functional performance during caloric restriction.