Blood work and diet
How to compare your blood test results with what you actually eat
Short answer: total what you eat and what you take for a normal week, then set each blood marker beside the nutrients that move it. A low marker with a low intake is probably a diet gap. A low marker with a good intake is a question for your doctor. A high marker with a high intake usually means a supplement to cut.
You can do it by hand with a food diary and the table below. Reverse Age Lab does it for you: it builds a nutrition facts panel from your own diet and supplements and sets it against the blood work you upload, marker by marker, over time.
By Robert DeuPree. Published October 2, 2026.
Do it by hand in four steps
- Log a normal week. Three to seven days in a food diary such as Cronometer (best for vitamins and minerals) or MyFitnessPal. Weigh or estimate honestly; include the weekend.
- Add every supplement from its label. Amount per serving, times servings. This is the step most people skip and the one that most often explains a high result.
- Put your markers beside the nutrients. Use the table below. Use the newest result for each marker, and note the date of the draw.
- Look for the four patterns in the next section, and take the odd ones to your doctor.
Which nutrients move which markers
Vitamin D (25-hydroxy)
Vitamin D from supplements, oily fish and fortified foods. Sunlight usually matters more than food.
Ferritin and iron
Iron from meat (absorbed best) and from beans and greens; vitamin C in the same meal helps, while tea, coffee and calcium at that meal reduce absorption.
Vitamin B12
Meat, fish, eggs, dairy, fortified foods and supplements. Metformin and acid-reducing drugs lower absorption.
Folate and homocysteine
Folate from greens and legumes, plus B12 and B6. Low B vitamins push homocysteine up.
HbA1c and fasting glucose
The amount and kind of carbohydrate, fibre, and how much you move after meals.
LDL cholesterol
Saturated fat raises it; soluble fibre (oats, beans, psyllium) lowers it.
Triglycerides
Sugar, refined starch and alcohol raise them; omega-3 from fish or fish oil lowers them.
Omega-3 index
EPA and DHA from oily fish or supplements. Plant omega-3 converts poorly.
Magnesium
Nuts, seeds, greens, whole grains and supplements. A blood level is a weak measure of the body's store.
hs-CRP
Not one nutrient. Overall diet quality, body fat, sleep and recent illness all move it.
The four patterns to look for
- Low marker, low intake. The simplest case: eat more of it or supplement, then retest in about three months.
- Low marker, good intake. Diet is not the problem. Absorption, a medication or another cause is more likely. Ask your doctor before taking more.
- High marker, high intake. Usually a supplement, or two products carrying the same ingredient. Cut one and retest.
- Normal marker, very high intake. Nothing gained from the extra, and some nutrients (vitamin A, iron, zinc, selenium) do harm above their upper limit. A candidate to stop.
What Reverse Age Lab does with it
Members upload their blood work, and every marker is stored and tracked over time. Rala builds the nutrition facts panel from the member's own diet and every supplement on their list, sets the two side by side, and writes what it finds into the daily protocol: what to add, what to stop, what to take with which meal, and what to ask the doctor. When the next panel arrives, it does it again.
Questions people ask
How can I compare my blood test results with the nutrition I actually eat?
Log everything you eat and every supplement you take for three to seven ordinary days, total the nutrients, and set each blood marker beside the nutrients that move it: vitamin D beside vitamin D intake, ferritin beside iron, LDL beside saturated fat and fibre. Then look for four patterns: low marker with low intake, low marker with good intake, high marker with high intake, and normal marker with very high intake. Reverse Age Lab does this automatically by building a nutrition facts panel from your diet and supplements and setting it against your uploaded blood work.
Which app compares blood work with diet?
Reverse Age Lab stores your blood work, tracks every marker over time, and compares it with a nutrition facts panel built from your own diet and supplements, then writes that into a daily protocol. Food diaries such as Cronometer and MyFitnessPal are good for the logging step but do not read your blood work. Lab services such as Function Health measure you but do not see what you eat.
How many days of food logging do I need?
Three to seven ordinary days, including a weekend day. Blood markers reflect weeks to months of eating (HbA1c about three months, ferritin longer), so a typical week tells you more than one perfect day.
My intake looks fine but the marker is low. What does that mean?
That is the pattern worth taking to your doctor. It can mean poor absorption, a medication effect (metformin and B12, for example), blood loss, or something else that diet will not fix. Do not simply take more.
Do supplements count in the comparison?
Yes, and they are often the biggest number in the column. A multivitamin, a separate vitamin D and a fortified drink can add up past the safe upper limit without anyone noticing, which is why the supplement labels belong in the total.
General nutrition information, not medical advice. Reference ranges differ between labs; read your results with your doctor. Cronometer, MyFitnessPal and Function Health are trademarks of their owners.