Originally posted 2016-02-13 11:00:51.
In the past decade, the Paleolithic diet (or paleo diet) has gained considerable popularity due to its claimed health benefits.
However, it differs from official dietary recommendations in many ways. For example, it excludes all grains, dairy products and industrially processed food.
Several studies have investigated the health effects of the paleo diet. This meta-analysis examined its effects on metabolic syndrome.
Metabolic syndrome is a group of adverse conditions associated with abdominal obesity.
These include the following risk factors for type 2 diabetes and heart disease:
- Abdominal obesity.
- Elevated blood sugar.
- Elevated blood pressure.
- High blood triglycerides.
- Low HDL-cholesterol.
An underlying cause of metabolic syndrome is thought to be the modern processed diet, causing low-grade inflammation and insulin resistance.
For this reason, it is very likely that diets based on unprocessed, whole foods, like the paleo diet, may improve health among people with metabolic syndrome.
Scientists from Bahrain and the Netherlands did a meta-analysis of randomized controlled trials that compared the paleo diet with other dietary patterns.
Basic Study Design
The researchers conducted a meta-analysis of randomized controlled trials.
They combined results from many conceptually similar studies and performed new statistical analyses.
The researchers then compared these findings to control diets based on nutrition guidelines from around the world.
The main research question of this review was: Does adhering to a Paleolithic diet improve metabolic risk factors?
Finding 1: The Paleo Diet Improved Body Composition
The paleo diet resulted in greater improvements in body composition than the diets based on official health recommendations.
Below is an overview of how the paleo diet differed from the control diets in the short-term. The numbers represent the mean difference.
- Body weight: -2.69 kg (-5.9 lbs).
- Waist circumference: -2.38 cm (-0.94 in).
Supporting this, a few other trials have shown that going on the paleo diet may reduce body weight and improve body composition.
Bottom Line: The Paleolithic diet resulted in greater reductions in body weight and waist circumference than diets based on official health recommendations.
Finding 2: The Paleolithic Diet Reduced Heart Disease Risk
Compared to the control diet, the Paleolithic diet also improved several other risk factors for heart disease.
- Triglycerides: -0.40 mmol/L.
- Systolic blood pressure: -3.64 mm Hg.
- Diastolic blood pressure: -2.48 mm Hg.
HDL-cholesterol and C-reactive protein levels were also reduced, but the differences between the diets were not significant.
A few other human trials on the paleo diet have provided similar results.
Bottom Line: The Paleolithic diet resulted in greater improvements in heart disease risk factors than diets based on official nutritional recommendations.
Finding 3: Effects on Blood Sugar Control
The paleo diet resulted in significant reductions in both fasting blood sugar and insulin.
However, changes in blood sugar and insulin were not significantly different between diets.
One uncontrolled trial also showed significant improvements to blood sugar control on a paleo diet.
Bottom Line: The Paleolithic diet resulted in improvements in blood sugar control. However, the difference between diets was not significant.
How Does the Paleolithic Diet Improve Metabolic Syndrome?
There are several possible reasons why the paleo diet may have an advantage over conventional diets.
- Paleolithic nutrition contains almost no carbs that are high on the glycemic index. Eating lots of high-glycemic foods may increase low-grade inflammation and the risk of insulin resistance.
- Paleolithic diets contain no processed foods. They are exclusively based on whole foods, including fruits and vegetables.
- Paleolithic diets contain no refined vegetable oils. Many vegetable oils are high in omega-6 fats, and may cause unfavorable ratios between omega-3 and omega-6. This may cause chronic, low-grade inflammation.
Bottom Line: Paleolithic diets do not contain any processed foods or foods that are high on the glycemic index. This may help prevent low-grade inflammation and reduce the risk of insulin resistance.
This meta-analysis appears to be well designed and not have any serious limitations. The control diets were also relatively similar.
However, the included studies had a few potential limitations:
- Most of the studies had few participants and were short in duration.
- The paleo diet prescribed in the studies may not accurately represent what “paleo” eaters consume in the real world.
- In three of the studies, the dietary intervention was in the form of advice and recommendations. Compliance may have been an issue in some of these studies.
- None of the included trials were fully blinded. This might have affected their results.
- Although the present meta-analysis tried to standardize the time-point data, the duration still ranged from 2 weeks to 6 months.
- Although the test and control diets in all 4 studies were reasonably similar, there were some differences. Even slight variations in macronutrient composition may have strong effects on health outcomes.
- One of the included trials had a baseline imbalance. Participants in the Paleolithic group had significantly worse outcome values at the start of the study compared to the control group.
- Only one study reported adverse effects, and none of them assessed quality of life.
Summary and Real-Life Application
In short, the study shows that a paleo diet may have moderate benefits for metabolic syndrome.
However, the authors of the article believe that more evidence is needed before Paleolithic nutrition can be recommended in official guidelines.
Additionally, it is debatable whether total avoidance of dairy and grains is necessary, or even advantageous, for optimal health.
That being said, it is clear that avoiding processed foods and adhering to a diet based on whole foods is sound nutritional advice.