A site that lists only the encouraging findings is advertising. This is the other half.
The only systematic review of eating solely animal foods found nine human studies in total — five case reports, two surveys of social media users, one exploratory study and one modelling exercise — and judged the evidence very limited. Its authors concluded that long-term adherence cannot currently be recommended. They flagged specific risks, and those are worth going through one at a time.
Nutrient shortfalls
The review identified likely gaps in vitamin C, vitamin D, calcium, magnesium, iodine and fibre.
Some of these are more arguable than others. Fresh meat and offal contain vitamin C, and there is a reasonable case that requirements fall when carbohydrate is very low — but “reasonable case” is not the same as “settled”, and scurvy is not a theoretical illness. Calcium is harder to get without dairy. Iodine without fish or dairy is harder still. Magnesium is a common shortfall even on ordinary diets.
The practical answer is variety — organ meat, fish including the small bones, shellfish, and dairy if your version allows it — plus bloods rather than guesswork.
Cholesterol
LDL and total cholesterol commonly rise on this way of eating, sometimes a great deal. This is well documented and it is the single most important thing to monitor.
What it means is genuinely debated. Some researchers argue that a rise in the context of low triglycerides and high HDL carries different implications from the usual picture; cardiology guidelines do not currently agree. You do not have to settle that argument. You do have to know your numbers, and discuss them with a doctor rather than with the internet.
Get a lipid profile before you start. Without a baseline, a later result tells you much less.
The first two weeks
Most people feel worse before they feel anything else: headache, fatigue, poor concentration, irritability, cramps. It is largely fluid and electrolytes — salt, potassium and magnesium shift when carbohydrate drops — and it usually passes within a fortnight.
Worth saying plainly on a site about mood: feeling flat and irritable for a fortnight is not a good trade for someone whose mood is already low. That is a reason to do this with a doctor’s knowledge, and a reason to stop if it does not settle.
Bowels
No fibre means bowel habits change. Some people find constipation, others the opposite. It is common, it is not dangerous in itself, and it is the sort of thing people quietly put up with rather than mention.
Medication
This is the part that can genuinely harm you.
- Diabetes medicines — insulin and sulfonylureas especially — can cause dangerously low blood sugar when carbohydrate drops sharply. Doses often need changing. This must be done with your prescriber, in advance.
- Blood pressure medicines may need review, as blood pressure often falls.
- Lithium levels are affected by fluid and sodium balance, both of which shift on this diet.
- Diuretics compound the fluid and electrolyte changes.
None of that is a reason for panic. All of it is a reason to tell your doctor before you start rather than after.
Who should not do this without specialist advice
Anyone who is pregnant or breastfeeding. Anyone with type 1 diabetes. Anyone with liver, kidney or pancreatic disease, or a disorder of fat metabolism. Anyone who has had an eating disorder. Anyone underweight. Anyone taking the medicines listed above.
What to ask for
A conversation and a baseline: full blood count, lipid profile, liver and kidney function, HbA1c, vitamin D, B12, folate, ferritin and thyroid function is a reasonable list to discuss — your GP may not agree to all of it, and that is their call to make.
Then repeat the lipids after about three months.
Where to go next
General education, not a diagnosis and not a treatment. If your mood has been low for weeks, your GP is the next step.
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