Blood tests and diet: how to read your results and what exactly to change on your plate

Bilberry Guide · updated: 22 Jul 2026 · approx. 13 min read

Most people pick a diet backwards: first the name ("keto", "Mediterranean", "IF"), then the search for justification. It should be the other way around — your blood test results are the best guide to what your body is missing and what's harming it. This guide walks through the most commonly tested markers and shows, marker by marker, which changes in your eating have a documented effect on the number.

Before you look at any single marker

Three rules for reading results that will save you panic and wrong conclusions:

"Within range" doesn't mean "optimal". A reference range is the interval that covers most of the population — not the interval where you feel your best. Ferritin at 12 with a range of "10–200" is technically within range, but for many people it means iron stores are running on empty.

A trend means more than a point. A single measurement is a snapshot — affected by hydration, sleep, infection, even the time of day the blood was drawn. Two or three measurements weeks apart show a direction. That's why results are worth collecting in one place instead of a drawer.

One marker is not a diagnosis. Markers are read in sets: iron together with ferritin and a full blood count; glucose together with insulin or HbA1c; ALT together with AST and GGT. A single number outside the range most often means "recheck and consult", not "you have a disease".

Ferritin and iron: energy, hair loss, breathlessness

Ferritin is your iron store — and usually the first marker to fall, long before a blood count shows anemia. The symptoms of low ferritin tend to be vague: chronic fatigue, reduced stamina, hair loss, cold hands and feet, brain fog.

What to eat when ferritin is low:

Iron comes in two forms with completely different absorption. Heme iron (meat, organ meats — especially liver, fish) is absorbed at 15–35%. Non-heme iron (legumes, whole grains, pumpkin seeds, spinach, parsley) — only 2–20%, and heavily depending on what else shares the plate:

What not to do: don't supplement iron blindly, without a confirmed deficiency. Excess iron is toxic, and in people with undiagnosed hemochromatosis (the most common genetic disorder in people of European ancestry) supplementation does real harm. First the test result, then — with your doctor — the dose.

Vitamin D: the near-default deficiency

At northern latitudes skin makes almost no vitamin D from roughly October to April — low 25(OH)D there is the statistical norm, not the exception. From food, meaningful amounts come only from oily sea fish (herring, salmon, mackerel), eggs and fortified products — and usually not enough.

In practice: eat oily fish 1–2 times a week (you get omega-3s in the bargain — see the lipid panel), and set a D3 supplement dose with your doctor based on your result — it is one of the vitamins that is easy to overdo, so we leave the numbers to them. One important detail: vitamin D is fat-soluble — take it with a meal that contains fat, not on an empty stomach with water.

B12 and folate: non-negotiable on plant-based diets

Vitamin B12 occurs only in animal products — on a vegan (and often a vegetarian) diet, supplementation isn't an option, it's a necessity. A deficiency develops insidiously over months (the liver holds reserves), and it can damage nerves before hemoglobin ever drops. Watch out for masking: a high folate intake can "improve" the blood count while the B12 deficiency continues.

Folate is found in leafy green vegetables, legumes and beets — for most people a balanced diet is enough; the exception is pregnancy and planning for it, where supplementation is standard care (to be agreed with your doctor).

Lipid panel: LDL, HDL, triglycerides

This is where diet has its best-documented power. Three numbers, three different levers:

LDL ("bad cholesterol") responds to fat quality and fiber. The most effective moves: swap part of your saturated fat (butter, lard, fatty meat, palm oil in sweets) for unsaturated (olive oil, canola oil, nuts, avocado); add soluble fiber — oats, ground flaxseed, apples, legumes, or psyllium husk. Each of these steps is genuinely worth several to a dozen-plus percent off LDL; together — often as much as a low-dose statin. Eggs affect LDL less than saturated fat does, but the response is individual.

Triglycerides respond to sugar and alcohol. High TG is usually not "too much fat" but too much simple sugar (sweets, juices, sugary drinks) and alcohol — plus a calorie surplus. Cut those three things, add oily sea fish (omega-3 EPA/DHA directly lower TG), and the number can fall by tens of percent within a few weeks.

HDL responds best to movement. Diet has limited room here (olive oil, nuts and quitting smoking help); the strongest lever is regular exercise and weight loss.

Glucose, HbA1c, insulin: before diabetes develops

Fasting glucose of 100–125 mg/dl is prediabetes — the moment when diet works best and can reverse the process. HbA1c shows the average of ~3 months, and fasting insulin (with the HOMA-IR calculation) detects insulin resistance years before glucose ever crosses the line.

What actually works:

1. Losing 5–10% of body weight — the strongest single factor for improving insulin sensitivity; how to pick the pace is covered in our article on calories for weight loss.
2. Meal composition: carbohydrates always in the company of protein, fat and fiber; low-glycemic-index foods (whole grains, legumes) instead of "fast" carbs. Even the order of eating matters: vegetables and protein before carbohydrates flatten the post-meal glucose spike.
3. Movement after meals: a 10–15 minute walk after your main meal noticeably lowers blood glucose — muscles take up glucose without needing insulin.
4. Liquid calories out: juices and sugary drinks are the fastest route to high spikes — and the easiest thing to cut.

TSH and the thyroid: iodine, selenium, iron

Elevated TSH (hypothyroidism) is first and foremost a matter for your doctor — but diet plays a supporting role. The thyroid needs iodine (sea fish, dairy, iodized salt — iodized salt covers a lot of ground in many countries), selenium (1–2 Brazil nuts a day are entirely enough — more is not better, selenium is easy to overdose) and iron — low ferritin impairs the synthesis of thyroid hormones, so those two problems often have to be fixed together.

If you take thyroid medication, coffee, dairy, soy and calcium/iron supplements can reduce how well it is absorbed — so when to take it, and how far from meals, is your doctor's call, with the details in your product's leaflet. Raw cruciferous vegetables (cabbage, broccoli) in sensible amounts are not a problem, especially with a good iodine supply.

Uric acid: gout starts on the plate

Elevated uric acid isn't just a gout risk — it also correlates with hypertension and metabolic syndrome. The three biggest dietary levers: fructose from drinks (sugary drinks and juices raise uric acid faster than most of the "forbidden" meats), alcohol (especially beer — even the alcohol-free kind contains purines), purines from organ meats and some seafood. What helps: hydration, dairy, coffee and cherries; weight loss — but a gentle one, because crash fasting paradoxically raises uric acid.

Liver enzymes (ALT, AST, GGT): the liver likes boring

Mildly elevated ALT with the typical "belly + desk job" profile is most often fatty liver — nowadays called MASLD. The good news: the liver regenerates spectacularly. What works above all is weight loss (even 5–7% makes a difference, 10% can reverse the fat buildup), a radical cut in alcohol and simple sugars (especially liquid fructose). Coffee — 2–3 cups a day — has surprisingly good data as a protective factor for the liver.

Magnesium, potassium, sodium: the calm before the cramp

Magnesium (nuts, seeds, whole grains, dark chocolate, legumes) and potassium (vegetables, potatoes, tomatoes, bananas, legumes) are markers that are rarely dramatically bad but often suboptimal — especially on a diet dominated by processed foods, which over-salts at the same time. The direction is always the same: more unprocessed plants, fewer products with a label. That automatically improves the sodium-to-potassium ratio — one of the strongest dietary factors in blood pressure.

Putting it together: from results to a meal plan

The bottom line is this: your test results are the best diet brief there is — but only if someone actually translates them onto the plate. The typical scenario looks different: the printout lands in a drawer, and the diet keeps running "off the internet".

In Bilberry that chain is closed: you upload a photo or PDF of your results, AI reads the markers (you confirm every value — nothing saves itself), and the system turns deviations into nutrition priorities that firmly shape your weekly meal plan: with low ferritin, the planner reaches for iron-rich foods and makes sure vitamin C comes along; with high triglycerides, it limits simple sugars and adds oily fish. Follow-up tests land on a timeline, so you can see whether the changes on your plate are moving the numbers.

Frequently asked questions

How often should I get tested? As a rule of thumb: a basic panel (full blood count, lipid panel, glucose, TSH, ALT, creatinine, ferritin, vitamin D) once a year, and the markers you're working on through diet — every 8–12 weeks. Agree the exact list and frequency with your doctor.

How long before diet changes my results? Triglycerides and glucose respond in 2–6 weeks, LDL in 4–8, HbA1c by its nature needs ~3 months, ferritin rises slowly (months). That's why retesting sooner than after 8 weeks usually makes no sense.

Should I supplement "just in case", without testing? No. Some deficiencies look identical to excesses (fatigue!), and iron or selenium in excess is outright harmful. The exception with a good safety profile is vitamin D at a moderate dose — but even there, one test a year lets you set the dose instead of guessing.

I have several abnormal results at once — where do I start? With a conversation with your doctor about priorities. On the diet side the good news is that most changes work "broadly": more unprocessed plants and fish, less sugar and alcohol improves the lipid panel, glucose, the liver and uric acid all at once.