The paleo diet isn’t inherently bad for you, but it carries real trade-offs that depend on how strictly you follow it and how long you stick with it. Short-term, it can improve cholesterol, reduce inflammation, and help with weight loss. Long-term, cutting out dairy, grains, and legumes creates nutrient gaps that are hard to fill, and most people abandon the diet within a year anyway.
What the Paleo Diet Actually Does Well
Paleo’s core principle is solid: eat whole foods, skip processed ones. A meta-analysis of eight randomized controlled trials found that people on a paleo diet saw modest but meaningful drops in LDL (“bad”) cholesterol compared to people eating other healthy diets. The diet also lowered triglycerides, blood pressure, and waist circumference in those same trials.
There’s decent evidence on inflammation, too. A large study of over 4,000 people in the Malmö Diet and Cancer cohort found that closer adherence to paleo-style eating was linked to lower C-reactive protein, a key marker of chronic low-grade inflammation. This tracks with what we know about diets that emphasize vegetables, fruits, nuts, and lean protein while cutting out refined sugar and ultra-processed food.
Blood Sugar Benefits Are Overstated
Paleo is often marketed as especially good for blood sugar control, but the evidence doesn’t support that claim when you compare it to other reasonable diets. A meta-analysis of four trials involving 98 people with impaired glucose metabolism found no significant difference between paleo and other healthy diets for fasting glucose, insulin levels, HbA1c (a three-month blood sugar average), or insulin resistance. The diet isn’t worse for blood sugar, but it’s not the standout performer its advocates suggest.
The Calcium and Iodine Problem
This is where paleo starts to look more concerning. By eliminating dairy entirely and restricting grains, the diet consistently falls short on several critical nutrients. Short-term studies show calcium intake dropping well below recommended levels for healthy adults. That’s compounded by two things working against you at once: paleo’s high protein content increases the amount of calcium you lose through urine, and without dairy, you also lose a major source of vitamin D, which your body needs to absorb calcium in the first place.
Iodine is another serious gap. One study tracking people on a paleo-style diet (30% of calories from carbohydrates) found that moderate iodine deficiency rose from 15% of participants to 73% after just six months. Iodine is essential for thyroid function, and most people get it from iodized salt, dairy, and bread, all of which paleo limits or eliminates. Across various low-carbohydrate diets, intakes of thiamine, folate, magnesium, calcium, iron, and iodine all decreased significantly, ranging from 10% to 70% below baseline levels.
Bone Health Over Time
The calcium and vitamin D shortfalls raise a specific long-term concern: bone density. When your dietary calcium is chronically low and your protein intake is high enough to drive extra calcium out through your kidneys, you’re creating conditions for bone demineralization. This can increase the risk of osteoporosis and osteopenia over years, particularly for postmenopausal women and older adults. Eating more calcium-rich vegetables like broccoli, kale, and bok choy can partially offset this, but few paleo followers eat enough of these foods to fully replace what dairy provides.
Kidney Concerns for Some People
Paleo diets typically push protein intake to 20-25% or more of total calories. For people with healthy kidneys, this likely isn’t a problem. But a significant number of adults have early-stage kidney disease without knowing it, particularly those with diabetes, obesity, or high blood pressure. Research published in Nephrology Dialysis Transplantation found that people consuming 1.2 grams of protein per kilogram of body weight per day experienced kidney function decline at twice the rate of those eating less than 0.8 grams per kilogram. For someone weighing 180 pounds, that threshold is roughly 98 grams of protein daily, an amount easy to exceed on paleo.
People at higher risk for kidney disease, including those with diabetes, obesity, high blood pressure, or a solitary kidney, are advised to keep protein below 1.0 gram per kilogram per day. Paleo routinely exceeds that.
Your Gut Bacteria Change, and Not for the Better
One of the less obvious downsides involves your gut microbiome. A study comparing long-term paleo followers to people eating a standard balanced diet found significant reductions in Bifidobacterium and Roseburia, two bacterial groups that produce butyrate, a fatty acid that feeds the cells lining your colon and helps regulate inflammation. These reductions were tied to lower grain consumption and lower carbohydrate intake overall, not to fiber intake alone.
Interestingly, overall microbial diversity (the total variety of gut bacteria) didn’t differ significantly between paleo followers and controls at either the species or genus level. The concern isn’t that paleo wipes out your microbiome diversity. It’s that it specifically depletes beneficial bacteria known to play protective roles in gut health.
What You Lose by Cutting Grains and Legumes
Paleo’s blanket ban on grains and legumes removes foods with strong evidence of health benefits. Whole grains contain fiber, vitamins, minerals, lignans, and protective plant compounds concentrated in the bran and germ. These components are stripped away in refined grains, which is why “avoid processed grains” and “avoid all grains” are very different recommendations with very different health consequences.
Legumes, including beans, lentils, and chickpeas, are among the most consistently health-promoting foods in nutrition research. They’re high in fiber, resistant starch, and plant protein while being low in fat. The paleo rationale for excluding them, that they contain antinutrients like lectins and phytates, doesn’t hold up well. Cooking neutralizes most lectins, and phytates actually function as antioxidants at the levels found in a normal diet.
How It Compares to the Mediterranean Diet
A large study using data from the NHANES cohort compared paleo-style and Mediterranean-style eating patterns and their association with mortality. Both diets were linked to lower risk of death from all causes, cancer, and cardiovascular disease. But the Mediterranean diet showed stronger protective effects across every category. People scoring highest on Mediterranean diet adherence had a 37% lower risk of all-cause mortality compared to those scoring lowest, while the highest paleo adherence was associated with a 23% lower risk. For cardiovascular death specifically, the Mediterranean pattern showed a statistically significant 32% reduction; paleo’s 22% reduction didn’t quite reach statistical significance.
The key difference is that the Mediterranean diet includes whole grains, legumes, and moderate dairy, capturing the benefits of whole foods without the nutrient gaps that strict paleo creates.
Most People Don’t Stick With It
Sustainability matters because a diet only works if you can maintain it. In a real-world weight loss trial where participants chose their own diet, only 18.4% selected paleo in the first place, the lowest of the three options offered. Of those who did choose it, just 35% were still following it at 12 months. That’s dramatically lower than the Mediterranean diet (57% adherence) and intermittent fasting (54% adherence) at the same time point. The restrictiveness of cutting out entire food groups, including bread, rice, beans, cheese, and yogurt, makes paleo one of the hardest dietary patterns to sustain.
Long-term clinical data on paleo remains limited partly for this reason. Researchers have difficulty keeping participants on the diet long enough to study multi-year outcomes, which means many of the long-term risks (bone density loss, kidney effects, microbiome shifts) are projected from shorter studies rather than directly observed over decades.
The Bottom Line on Risk
Paleo isn’t dangerous in the short term for most healthy adults, and its emphasis on whole foods over processed ones is genuinely good advice. The problems emerge with strict, long-term adherence: calcium and iodine deficiencies, reduced beneficial gut bacteria, potential bone and kidney risks, and the loss of well-studied protective foods like whole grains and legumes. A looser version of paleo that keeps some dairy, includes legumes, and doesn’t treat all grains as toxic would capture most of the benefits while avoiding the most significant downsides.