Science: what seven months of contest prep did to a natural bodybuilder
A 2025 study tracked a drug-free athlete for 31 weeks: fat fell from 17.9 to 4.2 kg while most muscle was kept — but bone density dropped too.
How does a long diet before a show change a natural athlete’s body? A case study published in 2025 in the journal Applied Sciences followed a male natural bodybuilder through 31 weeks — about seven months — of preparation, measuring him with a DEXA scan and blood tests at the start, at the midpoint and one week before the contest.
The numbers
Fat mass: 17.9 kg → 13.1 kg → 4.2 kg
Lean (muscle) mass: 69.9 kg → 68.2 kg → 66.7 kg
Energy intake fell gradually by 27.6%, while daily activity rose by 169%
Protein intake stayed almost the same; carbohydrates were cut step by step
In total he lost about 16.9 kg, and roughly four-fifths of it was fat — a good result that matches the classic advice to diet slowly and keep protein high.
The warning sign: bones
The study also found that the bones lost out: bone mineral content fell by 1.2% in the first half of the preparation and by a further 3.5% in the final weeks, and bone density decreased as well. A long, deep diet affects more than appearance — recovery after the show, and bone health in particular, deserve real attention.
Takeaways for athletes
Plan a long preparation and lose weight gradually
Keep protein intake high throughout the diet
Don’t stay in a deep deficit longer than necessary — and plan a proper recovery phase after the competition
Source: Applied Sciences 2025, 15(1), 79 — doi.org/10.3390/app15010079
