Week 7 is day 49: on a four-week ladder that is week 3 of dose step 2, and — at the seven-day half-life this class runs on — 7 half-lives in. Steady state is about five half-lives, so day 35 is where the concentration stops climbing on its own. Day 49 is 2 weeks past it, which means the level is no longer the variable. That distinction is most of the question: at week 3 of a step, an effect that is still accumulating is indistinguishable from one that is not resolving unless you know which side of day 35 you are on. Fatigue at any week has at least three candidate sources — the energy deficit, the fall in micronutrient intake that rides along with it, and the agent itself — and only the first two are cheaply measurable. Dose decisions are made under supervision, and nothing here is medical advice.
Answer first: fatigue in this context is usually an energy-intake problem before it is a drug effect, and the arithmetic is the first place to look.
Carbohydrate intake specifically affects training performance and perceived energy at a given total intake, which is why very low carbohydrate approaches feel worse in the gym at matched energy.
Fatigue that appeared abruptly, rather than gradually with the deficit, is a different pattern and points away from intake.
Energy deficits above roughly a thousand kilocalories a day are associated with measurable reductions in resting metabolic rate, spontaneous activity and subjective energy in controlled studies.
The caveat is that fatigue with breathlessness, chest symptoms or sudden onset needs assessment rather than dietary adjustment.
Weigh three days of intake honestly. That answers this most of the time.
edited 29 Jul 2024 by nominal_ten — clarified the distinction between purity and content
6Worth adding that the area postrema explanation also predicts why it settles. – Dr_Jonas_Halvorsen 8 months ago add a comment