I also think heart disease and gout are potential problems in the carnivore diet. But also cancer and malnutrition - there are a lot of nutrients proven to protect against cancers that are found in vegetables and fruits (e.g. berries), and also many are produced by gut bacteria when they are feed indigestable fibers (which are counted as carbohydrates)

This is what I think I know (I could be wrong of course, apparently I need to add disclaimers to everything I say now-a-days even though it should be obvious):

This data comes from dozens of sources I could not easily cite at this point. Much of the expert opinions come from thousands of studies, careful evaluation of which ones are good (only about 15%) and which ones matter most (maybe only 2%).  Anybody can "find a study" that says anything they want to hear, so be extremely careful about making conclusions from just 1 or 2 studies.  Many studies show LDL lowering reduces mortality, here is one just for kicks, but do not just accept single studies like this or any other:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9812424/

Heart disease
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Heart disease seems to be caused by:

1. Unmodifiable factors:  Age, maleness, family history and other genetic components
2. The concentration of ApoB lipoprotein in your bloodstream, integrated over time (high concentrations for short time periods don't add much to this integral)
3. Modulated by hypertension (higher blood pressure increases the rate)
4. Modulated by inflammation (reducing inflammation in the endothelial lining reduces the rate)
5. Made worse by other things that may damage your endothelial lining (smoking, elevated glucose for a long time, etc).

Most people don't get their ApoB measured, but LDL is a close proxy for it. The carnivore diet raises LDL. In some people (hyperresponders) it raises LDL massively.

Also it has been around forever - Egyptian Pharoahs had heart disease. The 'ice man' had heart disease. It's not caused by modern diets or "bread" it has been with us forever and not weeded out by evolution because it is a late-stage disease of aging.

Modern medicine has good solutions for preventing this disease which target LDL cholesterol. In particular:

1. If you are a hyper-producer of cholesterol, statin drugs very sigificantly lowers your LDL.
2. If you are a hyper-absorber of cholesterol, ezetimibe very sigificantly lowers your LDL.
3. Baby aspirin significantly lowers your inflammation (but may make gout worse)
4. Multiple drugs significantly lower your blood pressure (ACE inhibitors, ARBs, calcium channel blockers, beta blockers, diuretics).

Diet can also have a significant effect:

1. Lots of PUFAs (I know it's unpopular, but Canola oil is magically powerful against atherosclerosis), you can use nuts and seeds for these if you don't want seed oils.
2. Low saturated fat (which causes cholesterol), which lowers the level of ApoB
3. Low simple carbs (which raise triglycerides which also have an impact)

Weight loss has a significant positive effect, no matter how you do it.  If you lose weight on carnivore, the weight loss part of what you did was protective against atherosclerosis.

Exercise is also proven to have a sigificant effect, independent of any weight loss it may also provide.

Your body has a lot of ways to deal with atheromas in a "safe" way:  they tend to develop hard fibrous caps which protects you (they won't break and spill out and form a clot when they have a firm cap). Also, your blood vessels will form new tiny capillaries to carry blood around any narrowings.  And your blood vessels will expand to make more room when there is a narrowing.  So the lifetime buildup isn't really much of a worry as your body adapts to it. Exercise helps to maximize this adaptation.  The real worry is when a fresh atheroma with a soft cap bursts.  If you keep your inflammation and blood pressure down and your diet good, you can avoid these fresh atheromas and live a long life, even if you can't "reverse" heart disease (some doctors claim they can revese it, but most professionals have reason to doubt that. I also doubt it is reversable).

Gout
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This is a simple disease. You have too much uric acid, which has gotten to a high enough level that it crystallizes out into monosodium urate crystals. Your immune system can attack these crystals once they get into the wrong places (tiny areas in your joints, often your big toe).  They aren't attacked right-off-the-bat and by the time you have a gout attack you usually have quite a lot of crystal build-up.

The cause is either (1) Too much uric acid production, either (a) too many purines in your diet, or (b) too much break down of your body's tissues, or (2) your kidneys aren't filtering out the uric acid fast enough.  Some people turn over cellular material rapidly (1b) or don't have good kidney function (2), but eating a high purine diet can cause it all on it's own.

Purines are essentially from DNA.  The amount of purines you eat are proporational to the number of cells you eat.  Baby spinich has high purines compared to adult spinach because the cells are smaller. Same with baby fish vs adult fish.  Organ meat has more smaller cells.  Yeast is tons of tiny cells.  Eggs are one giant cell with essentially no purines. Milk isn't cellular and has no purines.

Gout isn't dangerous and is reversible (modulo any joint damage it caused that persists), but it is painful and best avoided.