The paleo diet is one of the most popular diets.

However, not all health professionals and mainstream nutrition organizations support it.

While some say it’s healthy and reasonable, others believe it may be harmful. Scientific studies can help us decide.

This article looks at five studies on the paleo diet, examining its effects on body weight and various health markers.

The paleo diet aims to recreate the eating pattern that human hunter-gatherers presumably followed. Supporters argue that it’s a healthy option, as there’s no evidence that hunter-gatherers experienced the same diseases that modern humans do.

The diet includes unprocessed animal and plant foods, including meat, fish, eggs, vegetables, fruits, nuts, and seeds.

It shuns processed foods, sugar, dairy products, and grains, although some versions allow foods like dairy and rice.

The following studies all looked at how the paleo diet affected human health. The research is published in respected, peer-reviewed scientific journals.

1. Lindeberg S, et al. A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease. Diabetologia, 2007.

Details. This study involved 29 males with heart disease and high blood sugar or type 2 diabetes. For 12 weeks, 14 participants followed a paleolithic diet while 15 followed a Mediterranean-like diet. There were no calorie restrictions.

The researchers focused mainly on the following outcomes: glucose tolerance, insulin levels, weight, and waist circumference.

Glucose tolerance. The glucose tolerance test measures how quickly the body clears glucose from the blood. It’s a marker for insulin resistance and diabetes.

This graph shows the difference between the groups. The solid dots are the baseline, and the open dots are after 12 weeks on the diet. The paleo group is on the left, and the control group is on the right.

As the graphs show, only the paleo diet group saw a significant improvement in glucose tolerance.

Weight loss. Both groups lost a significant amount of weight. Participants in the paleo group lost an average of 11 pounds (5 kg). Those following the Mediterranean diet lost 8.4 pounds (3.8 kg), on average. The loss was significant in both groups, but the difference between the groups was not statistically significant.

Waist circumference. The paleo diet group experienced a 2.2-inch (5.6-cm) reduction in waist circumference, on average, compared with 1.1 inches (2.9 cm) in the Mediterranean diet group. The difference was statistically significant.

A few important points:

  • The 2-hour area under the curve (AUC) for blood glucose fell by 36% in the paleo group, compared with 7% in the control group.
  • All members of the paleo group had normal blood sugar levels after 12 weeks, compared with 7 of 15 patients in the other group.
  • The paleo group consumed 451 fewer calories per day, without intentionally restricting calories or portions. They consumed 1,344 calories, on average, while the Mediterranean group consumed 1,795.

Conclusion. A paleolithic diet may improve measures of waist circumference and glycemic control, compared with a Mediterranean-like diet.

2. Osterdahl M, et al. Effects of a short-term intervention with a paleolithic diet in healthy volunteers. European Journal of Clinical Nutrition, 2008.

Details. Fourteen healthy medical students followed a paleolithic diet for 3 weeks. There was no control group.

Weight loss. The participants lost an average of 5 pounds (2.3 kg), their body mass index (BMI) decreased by 0.8, and waist circumference decreased by 0.6 inches (1.5 cm).

Other markers. Systolic blood pressure went down by 3 mmHg.

Conclusion. The participants lost weight and slightly reduced their waist circumference and systolic blood pressure.

3. Jonsson T, et al. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: a randomized cross-over pilot study. Cardiovascular Diabetology, 2009.

Details. In this crossover study, 13 individuals with type 2 diabetes followed two diets — a paleolithic diet and a typical diabetes diet — each for 3 months.

Weight Loss. Participants on the paleo diet lost 6.6 pounds (3 kg) more and lost 4 cm (1.6 inches) more off their waistlines, compared with the diabetes diet.

Other Markers:

  • HbA1c. This measure of 3-month blood sugar levels decreased by 0.4%, falling more among those on the paleo diet than among those on the diabetes diet.
  • HDL (good) cholesterol. HDL cholesterol levels rose by 3 mg/dL (0.08 mmol/L) on the paleo diet, compared with the diabetes diet.
  • Triglycerides. Levels fell by 35 mg/dL (0.4 mmol/L) on the paleo diet, compared with the diabetes diet.

Conclusion. The paleo diet caused more weight loss and improvements in several cardiovascular risk factors, compared with a diabetes diet.

4. Frassetto, et al. Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet. European Journal of Clinical Nutrition, 2009.

Details. Nine healthy individuals consumed a paleolithic diet for 10 days. Calorie control ensured they did not lose weight. There was no control group.

Health effects:

  • Total cholesterol: went down by 16%
  • LDL (bad) cholesterol: went down by 22%
  • Triglycerides: went down by 35%
  • Insulin AUC: went down by 39%
  • Diastolic blood pressure: went down by 3.4 mmHg

5. Ryberg, et al. A Palaeolithic-type diet causes strong tissue-specific effects on ectopic fat deposition in obese postmenopausal women. Journal of Internal Medicine, 2013.

Details. Ten healthy females with a BMI over 27 consumed a modified paleolithic diet for 5 weeks. There was no control group. The researchers measured their liver fat, muscle cell fat, and insulin sensitivity.

Weight loss. The participants lost an average of 9.9 pounds (4.5 kg) and experienced a 3.1-inch (8-cm) reduction in waist circumference.

Liver and muscle fat. The fat contents of liver and muscle cells are a risk factor for metabolic disease. In this study, there was an average reduction in liver fat of 49%, but no significant effect on the fat content of muscle cells.

This graph shows how the fat content of liver cells decreased:

As you can see, those who had a lot of liver fat (fatty liver) had the most significant decrease.

Other effects:

  • Blood pressure: fell from an average of 125/82 mmHg to 115/75 mmHg, although it was only statistically significant for diastolic blood pressure (the lower number)
  • Fasting blood sugars: decreased by 6.35 mg/dL (0.35 mmol/L), while and fasting insulin levelsdecreased by 19%
  • Total cholesterol: decreased by 33 mg/dL (0.85 mmol/L)
  • Triglycerides: went down by 35 mg/dL (0.39 mmol/L)
  • LDL (bad) cholesterol: went down by 25 mg/dL (0.65 mmol/L)
  • HDL (good) cholesterol: decreased by 7 mg/dL (0.18 mmol/L)
  • ApoB: decreased by 129 mg/L (14.3%)

Conclusion. During the 5-week study, the women experienced weight loss and reductions in liver fat. They also had improvements in several important health markers.

This graph shows the amount of weight loss in the studies.

*In Lindeberg, et al the weight loss difference was not statistically significant (1).

The graph does not include the study by Frassetto, et al, as it controlled for calories to make sure the participants didn’t lose weight (4).

It’s worth noting the following:

  • None of the participants had instructions to restrict calories, but they spontaneously reduced calorie intake by 300–900 calories per day.
  • The participants ate fewer carbs and more protein than in their usual diet.

The graph below shows the effect on waist circumference. This is a marker for a type of visceral fat that accumulates around the organs, as well as a risk factor for various diseases.

The studies showed statistically significant reductions in waist circumference. Decreasing waist circumference may reduce the risk of diseases like diabetes and cardiovascular disease.

In the study by Ryberg, et al, participants lost an average 47% of liver fat after 5 weeks on the paleo diet, an effect that’s likely to improve health (5).

Four of the studies (studies 2­ to 5) reported changes in total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol, and blood triglycerides.

Two studies saw reductions in total cholesterol. However, in two others, the difference was not statistically significant (2, 3, 4, 5).

Two studies observed a statistically significant reduction in LDL (bad) cholesterol (4, 5).

Two studies noted a statistically significant difference in HDL (good) cholesterol. One study showed a decrease, the other an increase (3, 5).

All of the studies showed reductions in blood triglyceride levels, but the difference was not statistically significant in one study (2).

All of the studies looked at markers of blood sugar levels and insulin sensitivity.

However, the researchers used different measuring methods, so it’s not possible to compare the results in a graph.

The results of these studies suggest that the paleo diet can lead to improvements in insulin sensitivity and glycemic control, although the results were not always statistically significant (1, 2, 3, 4, 5).

Four of the studies (numbers 2–5 above) looked at blood pressure levels before and after the intervention.

Overall, the studies observed mild reductions in blood pressure.

However, the results were not conclusive:

  • In one study (number 2), the decrease in systolic blood pressure (the higher number) was statistically significant.
  • In studies 3–5, the decrease in diastolic blood pressure (the lower number) was statistically significant.

Overall, participants tolerated the paleo diet well, and there were no reports of adverse effects.

These studies had several limitations:

  • All were small, with the number of participants ranging from 9–29.
  • The studies did not last long, ranging from 10 days to 12 weeks.
  • Only 2 out of 5 studies had a control group.

Additionally, the paleo diet used in the studies is not the typical paleo diet that many people follow today.

It was a “conventional” paleo diet that restricted dairy and sodium, emphasized lean meats, and used canola oil.

Lean meats and canola oil aren’t very popular in the paleo community today, but the original book, “The Paleo Diet” by Dr. Loren Cordain, recommended these. All the studies used this version of the diet.

These studies are too small and too short in duration to form a definitive conclusion about the paleo diet.

However, the diet is growing in popularity, and research on its effectiveness continues. For example, in 2019 a systematic review and meta-analysis looked at findings from 1,088 articles. The results supported the use of the paleo diet in reducing weight, BMI, and waist circumference (6).

As researchers carry out larger and longer studies, more evidence may emerge to support the health benefits of the paleo diet.