Weight is an outcome. These are the inputs.

• Fatty acid and carbohydrate metabolism: How efficiently you are converting fuel to energy, and where that process is under strain.
• B-complex vitamins: Functional markers of B-vitamin status, relevant when reduced appetite lowers total food intake.
• Neurotransmitter metabolism: Pathways linked to mood, appetite regulation and energy.
• Oxidative stress and dysbiosis markers: Signs of cellular stress and gut-metabolic imbalance.
• Nutritional markers: Broader intake and utilisation signals drawn from your urine profile.

• Shannon diversity index: Diversity narrows when total intake and food variety fall, a common and unintended consequence of eating much less.
• Butyrate-producing species: Faecalibacterium prausnitzii and relatives. Butyrate is the main fuel for the cells lining the colon, and fibre intake tracks with their abundance.12
• Fibre-degrading capacity: Which fibres you tolerate. Directly relevant when appetite is reduced and every mouthful has to count.
• Protein and amino acid handling: Microbial contribution to how well dietary protein is used, which matters more when total protein is harder to reach.
• B-vitamin synthesis capacity: Microbial contribution to folate and B12 availability, read alongside the blood levels above.

• Protein intake and distribution: Grams per day and how evenly they are spread. The single most important number when appetite is reduced, and the one most often missed.
• Resistance training frequency: Sessions per week loading muscle against meaningful resistance. This is what determines whether weight lost is fat or fat plus muscle.
• Current medicines and supplements: Recorded so guidance is safe and consistent with what your doctor has prescribed. We do not change or advise on prescribed treatment.
• Rate of weight change: How fast, over how long. Faster is not better: rapid loss is associated with a greater share coming from lean tissue.
• Digestive tolerance: Nausea, constipation and reflux, recorded because they drive which foods get dropped, and dropped foods are where shortfalls begin.
• Sleep duration and regularity: Both are recorded, because both affect insulin sensitivity and next-day appetite.
• Weight history and previous attempts: What has been tried, what worked, and what happened afterwards. Context that changes what is worth recommending next.

Because the systems underneath have changed. Insulin sensitivity, muscle mass, appetite signalling, thyroid function, sleep and hormonal stage all influence what a given diet does to your weight, and all six drift with age. Measuring them tells you which lever is worth pulling instead of repeating the one that used to work.

The same three layers as anyone else: vivaMETABOLITE, vivaBIOME and a lifestyle assessment. Reduced appetite means a smaller total food intake, which makes a nutrient shortfall more likely, so the priority is tracking that alongside whether muscle is being preserved as you lose fat. This is nutritional support alongside your doctor’s care, not a substitute for it. Download a copy of our GLP-1 Compass whitepaper, a science-backed guide to optimising your GLP-1 experience.

The evidence is mixed and still developing. A network meta-analysis of 22 randomised trials found lean mass loss comprising roughly 25% of total weight loss, and a recent case series cited figures of 26–40% in trials; other studies using DXA have reported preserved lean mass and improved grip strength. Because losing muscle during any weight loss is undesirable, protein intake and resistance training are worth prioritising either way. Discuss any medicine with your prescribing doctor.

In the STEP 1 trial extension, participants regained two-thirds of their prior weight loss in the year after treatment and lifestyle intervention were withdrawn, and most cardiometabolic improvements reverted towards baseline. The practical implication is that the muscle, strength and habits built during treatment are what carry over. Any decision about starting or stopping is one for your prescribing doctor.

Biological drift is the slow change in cellular biomarkers that collectively result in chronic disease, and the symptoms relating to chronic disease as they develop. These could include weight gain, brain fog and energy loss. Drift happens inside the normal reference range, which is why standard testing often reads as normal.

Strength changes are measurable within six to eight weeks and fitness within eight to twelve. Fasting insulin, inflammatory markers and iron stores typically shift over three to six months, which is why vivaLAB re-tests every six months rather than chasing the scales weekly.