Does cutting out grains, dairy and legumes actually do anything?

Not on its own, in the one study built to find out. Fourteen adults with type 2 diabetes ate a paleo diet and a diabetes diet in turn. Calories were adjusted to keep weight steady, and the diets were matched for carbs, fat, protein and how much they raise blood sugar. There was no difference in long-term blood sugar (HbA1c) or in fructosamine, another blood sugar test. The authors concluded that the food groups paleo cuts out do not affect blood sugar control.

Is the ancestral reasoning supported?

The markers it predicts have been measured, and they did not move. The controlled study that tested gut leakiness, inflammation and the stress hormone cortisol found all three unchanged. The weight-steady study found no blood sugar effect. The benefits are real, and they come from eating less, not from removing foods that arrived with farming.

Does it work long term?

Over two years, mostly no. Fat loss was 6.5 kg against 2.6 at six months, and 4.6 against 2.9 at twenty-four months, no longer a clear difference. The liver fat advantage disappeared too. The study's own explanation is that people did not stick to the protein intake. What lasted through two years was the triglyceride advantage.

What do I need to watch?

Calcium and iodine, because cutting dairy removes the main source of both. The measured shortfalls were 292 mg and 48 micrograms a day. And muscle, if you are a man losing weight without training. In one study, diet alone cost men 2.6 kg of lean tissue, against 1.2 kg when weight training was added.

Elimination11 studies in people cited

Paleo

Q: Then why do people lose weight on it?

Because they eat less without trying. In the group whose blood sugar result is most quoted, the paleo group ate 5.8 megajoules (a unit of food energy) a day against 7.6 on the other diet. That is roughly 430 calories less, and they felt just as full. Eating 430 fewer calories a day at the same fullness is truly useful. It is also not the reason the diet's own story gives.

Written by Aaron CuhaReviewed Sep 2026

Also called: Palaeolithic diet, Primal, Ancestral eating

Cutting out grains, dairy and beans does nothing you can measure once weight and the mix of carbs, fat and protein are held steady. When people eat it freely, they eat about 430 calories a day less and feel just as full, and that is why it works.

What it actually is

Meat, fish, eggs, vegetables, fruit, nuts and seeds. Cut out: grains, dairy, beans and lentils, added sugar and processed oils. Unlike keto, it has no carb target. So a paleo diet can be high or low in carbs, depending on how much fruit and starchy roots like potatoes you eat.

How its fans say it works

The idea is that our bodies are built for the foods people ate before farming. On this view, grains, dairy and beans bring in compounds we handle poorly, and those drive inflammation, a leaky gut and metabolic disease. The idea is specific and testable. It predicts that removing those three food groups will improve health markers even when weight and calories stay the same. That has been tested.

What happened when calories were controlled

Best kind of study available: calories matched

Both groups ate the same number of calories, so a difference comes from what was in the diet, not how much people ate.

The core claim fails its cleanest test. When weight and the mix of carbs, fat and protein were held steady, cutting grains, dairy and beans made no difference to blood sugar control. Where controlled studies did find benefits, either the calorie control failed and people lost weight anyway, or there was no comparison group.

Genoni 2016 was a clean four-week head-to-head in 39 women, who ate as much as they wanted. Paleo lost 1.99 kg more, a clear difference. There was no difference between groups on any heart or metabolic marker. The paleo group also ate 292 mg a day less calcium and 47.9 micrograms a day less iodine.
Boers 2014 was meant to keep calories equal and failed at it. Despite efforts to keep weight steady, the paleo group lost 1.32 kg more, a clear difference. Blood pressure, cholesterol and triglycerides all improved against the comparison diet, and the authors report this held after adjusting afterwards for the weight loss nobody planned. In the same study, three things did not change: gut leakiness, inflammation and the stress hormone cortisol in saliva. Those are the three things the paleo idea says should move.
Masharani 2015 controlled and provided calories for 24 people with type 2 diabetes, and measured their response to insulin with a precise hospital test called a clamp. Both groups improved, with more benefit reported on paleo. The summary gives no numbers, so none are quoted here.
Fontes-Villalba 2025 is the direct test. 14 adults with type 2 diabetes ate each diet for four weeks, one after the other. Calories were adjusted throughout to keep body weight steady, and the diets were matched for carbs, fat and protein and for how much they raise blood sugar. Result: no difference in long-term blood sugar (HbA1c) or in fructosamine, a shorter-term blood sugar test. The authors concluded that the food groups paleo cuts out do not affect blood sugar control. It was small and short, and it is the most direct test that exists.
Frassetto 2009 controlled calories and provided food, but had only 9 people and no comparison group. Blood pressure, insulin response and cholesterol all improved against each person's own starting point over ten days. Without a comparison group, that describes what happened. It is not a comparison.

What happened when people just ate it

It works, and the studies pinned down why with unusual precision. Lindeberg 2007 studied people with heart disease and poor blood sugar control. Their blood sugar handling improved 26 percent on paleo against 7 percent on a Mediterranean-style diet. Then Jönsson 2010 published how much that same group ate: 5.8 megajoules (a unit of food energy) a day on paleo against 7.6 on the other diet. That is roughly 430 calories a day less, and people rated how full they felt the same on both. So they ate a lot less and felt just as full. Jönsson 2009 found long-term blood sugar down 0.4 points and weight down 3 kg against a diabetes diet. It said plainly that the paleo group ate fewer total calories, less calorie-dense food, fewer carbs, less saturated fat and less calcium, and food that raised blood sugar less. Ryberg 2013 found ten women ate 25 percent fewer calories and lost 4.5 kg over five weeks. Their liver fat fell 49 percent, while their whole-body response to insulin, measured with the clamp test, did not change. That is the honest story of this diet. Eating less without trying, while feeling just as full, is truly valuable. It is a different claim from the one the ancient-diet idea makes.

Protein, and whether it muddies the result

Protein runs high by design, and that is probably a real part of why people eat less. The two-year Umeå study has the sentence that explains where this research ends up: people in the paleo group did not stick to the protein intake. A strong start, then drift, then the groups end up the same. Muscle is the cost to watch. In a twelve-week study where everyone ate paleo freely, men in the diet-only group lost 2.6 kg of lean mass. Men who also trained three times a week lost 1.2 kg, a clear difference. Diet alone cost men lean tissue.

The measured intakes behind the protein figures are on the protein page.

What reliably moves

Measure	Direction	From
Calories eaten	Down by about 430 calories a day, at the same fullness	5.8 against 7.6 megajoules a day, in the same group whose blood sugar result is widely quoted, with the same fullness ratings. This is how the diet really works, and it is a good way.
Triglycerides (blood fats)	Down, and the longest-lasting result	Clearly better than the comparison diet at both six and twenty-four months in the Umeå study, after the weight advantage was gone. It was also the only marker that tracked how well people stuck to the diet, separate from weight loss.
Liver fat	Down sharply, then the groups caught up	Down 64 percent against 43 percent at six months, a clear gap. At twenty-four months it was 50 against 49 percent, and the gap was gone. The liver's response to insulin improved in the first six months, then got worse between six and twenty-four.
Blood pressure	Down	Top number down 9.1 and bottom number down 5.2 mmHg against the comparison diet, in a two-week study meant to keep calories equal, where people still lost 1.32 kg more than planned.
Calcium and iodine intake	Down, by design	292 mg a day less calcium and 47.9 micrograms a day less iodine in a four-week head-to-head. Cutting dairy without replacing the calcium is the expected result of the rule.
Gut leakiness, inflammation, stress hormone	No change	None of the three moved in the controlled study that measured them. All three are what the ancient-diet idea says should move.
Muscle in men who did not train	Down	2.6 kg lost on diet alone against 1.2 kg with supervised exercise three times a week, a clear difference between groups.

Long term, and serious health events

Two years, one study, and it shows drift rather than lasting results. In 70 obese women past menopause eating freely, fat mass fell 6.5 kg on paleo against 2.6 kg on the Nordic comparison diet at six months, a clear gap. At twenty-four months it was 4.6 against 2.9 kg, no longer a clear difference. The study's own explanation is one sentence: the paleo group did not stick to the protein intake. The liver fat advantage followed the same path and disappeared. What lasted two years was the triglyceride advantage. No paleo study has counted heart attacks, broken bones or deaths. Worth noting: the strongest studies here were paid for by Swedish public and charity funders with no company sponsor. That is unusual in this field, and it adds to their credibility, even where they found nothing.

Sources

Study in people2025
Randomised crossover controlled trial of dietary interventions for glycaemic control when body weight is kept stable
Journal of Nutritional Science
14 adults with type 2 diabetes tried each diet in turn. Calories were set to keep their weight steady, and the diets were matched for carbs, fat, protein and blood sugar load. Long-term blood sugar did not differ. Cutting out grains, dairy and beans did nothing on its own.
The direct test of the core claim. 14 adults with type 2 diabetes, crossover, energy adjusted to keep weight stable and diets matched for macronutrients and glycaemic load. No differences on HbA1c or fructosamine. Excluding grains, dairy and legumes did nothing of its own.
Study in people2009
Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet
European Journal of Clinical Nutrition
9 healthy people ate a paleo diet for ten days, with food given to them and calories controlled. Blood pressure, insulin response to a sugar test, and blood fats all improved against their own starting levels. There was no comparison group.
9 healthy volunteers, calories controlled and food provided, ten days, no control arm and no randomisation. Blood pressure, insulin response during glucose tolerance testing and lipids all improved against each participant's own baseline.
Study in people2015
Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes
European Journal of Clinical Nutrition
24 people with type 2 diabetes ate paleo or a comparison diet, with food and calories provided. Insulin sensitivity was checked with a precise hospital test. Both groups improved, with more benefit reported on paleo. The summary gives no numbers, so we quote none.
24 people with type 2 diabetes, calories controlled and provided, insulin sensitivity by euglycaemic clamp. Both arms improved with greater benefit reported on paleo. The abstract carries no numeric values, so none are quoted.
Study in people2014
Favourable effects of consuming a Palaeolithic-type diet on characteristics of the metabolic syndrome: a randomized controlled pilot-study
Lipids in Health and Disease
34 adults with signs of metabolic syndrome ate paleo or a comparison diet for two weeks. The diets were meant to have the same calories, but that failed: the paleo group lost 1.32 kg more. On paleo the top blood pressure number fell 9.1 and triglycerides fell 0.89. Gut leakiness, inflammation and the stress hormone cortisol did not change, and those are the three things the theory predicts.
34 adults, two weeks, designed as isoenergetic and it failed: weight fell 1.32 kg more on paleo (p = 0.012). Systolic pressure minus 9.1 mmHg, triglycerides minus 0.89 mmol/L. Nulls on intestinal permeability, inflammation and salivary cortisol, the three markers the mechanism predicts.
Study in people2007
A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease
Diabetologia
29 people with heart disease ate as much as they wanted of paleo or a Mediterranean-like diet for twelve weeks. Blood sugar after a sugar test fell 26 percent on paleo against 7 percent on the other diet, a clear gap. Waist size dropped 5.6 cm against 2.9 cm.
29 patients, twelve weeks, ad libitum. Glucose area under the curve minus 26 percent on paleo against minus 7 percent on the comparator, between-group p = 0.001. Waist minus 5.6 against minus 2.9 cm.
Study in people2010
A Paleolithic diet is more satiating per calorie than a Mediterranean-like diet in individuals with ischemic heart disease
Nutrition and Metabolism
This is the calorie data from that same study, and it explains a lot. People ate 5.8 MJ a day on paleo against 7.6 on Mediterranean, roughly 430 fewer calories a day. Yet they felt just as full on both.
The energy intake figures for that same cohort, and the key to the whole pattern. 5.8 MJ/day on paleo against 7.6 MJ/day on Mediterranean (p = 0.04), roughly 430 kcal/day less, with subjective satiety ratings the same in both groups.
Study in people2009
Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study
Cardiovascular Diabetology
13 people with type 2 diabetes tried paleo and a diabetes diet in turn, eating as much as they wanted. On paleo, long-term blood sugar fell 0.4 points, weight 3 kg and waist 4 cm compared with the diabetes diet. The paper says the paleo diet was also lower in calories, carbs, saturated fat and calcium.
13 patients with type 2 diabetes, crossover, ad libitum. HbA1c minus 0.4 percentage points, weight minus 3 kg, waist minus 4 cm against a diabetes diet. The paper states the paleo arm was lower in total energy, energy density, carbohydrate, glycaemic load, saturated fat and calcium.
Study in people2014
Long-term effects of a Palaeolithic-type diet in obese postmenopausal women: a 2-year randomized trial
European Journal of Clinical Nutrition
70 postmenopausal women with obesity ate as much as they wanted of paleo or a comparison diet for two years. At six months paleo was clearly ahead on fat loss, 6.5 kg against 2.6. By twenty-four months it was 4.6 against 2.9 kg, too close to call. The authors say the paleo group stuck poorly to its protein target.
70 obese postmenopausal women, ad libitum, two years. Fat mass minus 6.5 against minus 2.6 kg at six months (p < 0.001), then minus 4.6 against minus 2.9 kg at twenty-four months (p = 0.095, not significant). Verbatim: adherence to protein intake was poor in the paleo group.
Study in people2017
Benefits of a Paleolithic diet with and without supervised exercise on fat mass, insulin sensitivity, and glycemic control: a randomized controlled trial in individuals with type 2 diabetes
Diabetes/Metabolism Research and Reviews
32 people with type 2 diabetes ate as much paleo food as they wanted for twelve weeks. Some got standard exercise advice, and others did three supervised workouts a week. Long-term blood sugar fell about 1 point in both groups. Men who only changed their diet lost 2.6 kg of lean tissue, against 1.2 kg for men who also exercised.
32 people with type 2 diabetes, twelve weeks ad libitum paleo, randomised to standard exercise advice or three supervised sessions weekly. HbA1c fell about 1 percentage point in both. Men in the diet-only arm lost 2.6 kg of lean mass against 1.2 kg with exercise, p < 0.05.
Study in people2016
Cardiovascular, metabolic effects and dietary composition of ad-libitum Paleolithic vs. Australian Guide to Healthy Eating diets: a 4-week randomised trial
Nutrients
39 healthy women ate as much as they wanted of paleo or Australian healthy eating advice for four weeks. The paleo group lost 1.99 kg more, a clear gap, but no heart or blood marker differed between groups. The paleo group ate 292 mg less calcium and 47.9 micrograms less iodine a day.
39 healthy women, four weeks, ad libitum. Weight minus 1.99 kg greater on paleo (p < 0.001) and no differences in any cardiovascular or metabolic marker between groups. Paleo arm ate 292 mg/day less calcium and 47.9 micrograms/day less iodine.
Study in people2016
Strong and persistent effect on liver fat with a Paleolithic diet during a two-year intervention
International Journal of Obesity
At six months, liver fat fell 64 percent on paleo against 43 percent on the comparison diet, a clear gap. At twenty-four months it was 50 against 49 percent, so the gap was gone. The liver's response to insulin improved for six months, then got worse. 41 percent of people had no final liver fat measure.
Liver fat minus 64 percent against minus 43 percent at six months (p < 0.01), and at twenty-four months minus 50 against minus 49 percent, the difference gone. Hepatic insulin sensitivity improved in the first six months then deteriorated. 41 percent attrition on the primary measure.

What people report

These are things people say about their own eating. Nobody checked them, so they are not evidence. They are here because they tell you what to expect and what to watch for, which the studies do not. They cannot tell you whether anything works.

Less bloating and better digestion, reported often. That fits either the elimination or simply eating less processed food.
Feeling full on fewer calories, which is the effect the studies actually measured.
Easier to keep up socially than keto or carnivore, because carbs from fruit and starchy roots are allowed.
Cost, the most common practical complaint, since the diet leans on meat, fish and nuts.
Drifting back to grains and dairy over months. That matches the study data exactly: the advantage was gone by twenty-four months, and the study's own note was that people did not stick to the protein intake.
Some reports of worse performance in heavy training, blamed on eating fewer carbs in practice, even though the diet does not require that.

Sources: r/paleo and ancestral health groups, plus how well people stuck to the diet in the studies, which is better than most. One follow-up analysis found the share of paleo eating rose from 28 percent of calories at the start to 94 percent after twelve weeks with intensive support. Otherwise unchecked self-report.

Who this is wrong for

Anyone who will not replace the calcium and iodine from food. Cutting dairy removes the main source of both in most Western diets, and the measured shortfalls are 292 mg a day and 47.9 micrograms a day.
Anyone at risk of bone loss, especially women past menopause, without sorting out calcium and vitamin D. No paleo study has counted fractures.
Any man doing this for weight loss without weight training. In one study, diet alone cost men 2.6 kg of lean mass, against 1.2 kg with training.
Anyone who believes the ancient-diet reasoning is why it works. The one study that held weight and the mix of carbs, fat and protein steady found no effect on blood sugar control, and the three markers the idea predicts did not move.
Anyone for whom cutting beans and whole grains means cutting their cheapest sources of fibre, without a plan to replace them.

Questions

Does cutting out grains, dairy and legumes actually do anything?: Not on its own, in the one study built to find out. Fourteen adults with type 2 diabetes ate a paleo diet and a diabetes diet in turn. Calories were adjusted to keep weight steady, and the diets were matched for carbs, fat, protein and how much they raise blood sugar. There was no difference in long-term blood sugar (HbA1c) or in fructosamine, another blood sugar test. The authors concluded that the food groups paleo cuts out do not affect blood sugar control.
Then why do people lose weight on it?: Because they eat less without trying. In the group whose blood sugar result is most quoted, the paleo group ate 5.8 megajoules (a unit of food energy) a day against 7.6 on the other diet. That is roughly 430 calories less, and they felt just as full. Eating 430 fewer calories a day at the same fullness is truly useful. It is also not the reason the diet's own story gives.
Is the ancestral reasoning supported?: The markers it predicts have been measured, and they did not move. The controlled study that tested gut leakiness, inflammation and the stress hormone cortisol found all three unchanged. The weight-steady study found no blood sugar effect. The benefits are real, and they come from eating less, not from removing foods that arrived with farming.
Does it work long term?: Over two years, mostly no. Fat loss was 6.5 kg against 2.6 at six months, and 4.6 against 2.9 at twenty-four months, no longer a clear difference. The liver fat advantage disappeared too. The study's own explanation is that people did not stick to the protein intake. What lasted through two years was the triglyceride advantage.
What do I need to watch?: Calcium and iodine, because cutting dairy removes the main source of both. The measured shortfalls were 292 mg and 48 micrograms a day. And muscle, if you are a man losing weight without training. In one study, diet alone cost men 2.6 kg of lean tissue, against 1.2 kg when weight training was added.