There are many mixed opinions in nutrition science.
Dozens of studies are published every week, but most of them are of a low quality.
The studies most commonly promoted by the media are test-tube studies, animal studies or observational studies.
These studies have limited value on their own, and their results often completely contradict each other.
This has caused a lot of confusion about what constitutes evidence-based nutrition.
However, there are a few facts in nutrition that are truly backed by strong evidence.
These are supported by systematic reviews, meta-analyses or randomized controlled trials — the best types of studies we have.
Here are 14 nutrition facts that are supported by strong evidence.
1. Low-Carb Diets Promote Weight Loss
In fact, a detailed analysis of 17 randomized controlled studies found that overall, low-carb diets led to greater weight loss and reduction in heart disease risk factors, when compared to low-fat diets (10).
Low-carb diets appear to be particularly beneficial for people with metabolic syndrome, who carry excess weight around the middle and are at an increased risk of diabetes.
In a 12-week study of men with metabolic syndrome, the low-carb group lost nearly twice as much weight as the low-fat group. They also had a 20% average decrease in abdominal fat, compared to 12% in the low-fat group (7).
In many studies, the low-carb groups were allowed to eat unlimited protein and fat. One of the reasons low-carb diets work so well is that they tend to reduce appetite. This results in a spontaneous decrease in calorie intake (8, 9).
Bottom Line: Many controlled studies have shown that low-carb diets are very effective for weight loss. They also reduce many risk factors for heart disease.
2. Saturated Fat Doesn’t Cause Heart Disease
For several decades, it was believed that eating saturated fat raised the risk of heart disease.
The theory was that saturated fat raised blood cholesterol levels and led to blocked arteries, which caused heart attacks.
In response to warnings from health organizations, many people replaced whole-milk dairy products with low-fat and fat-free versions. They also exchanged natural fats like butter for margarine made from vegetable oil.
A 2014 review of 76 observational and randomized controlled studies with more than 650,000 participants found that those with a high saturated fat intake did not have an increased risk of heart disease (11).
However, the claim that eating saturated fat causes heart disease is not supported by the best available evidence to date.
Bottom Line: Comprehensive analyses of observational and controlled studies have found no convincing evidence that eating saturated fat causes heart disease.
3. Coffee and Green Tea Are Healthy Beverages
A lot of evidence suggests they are also among the healthiest.
One analysis of 41 studies found that the most effective dosage to maximize caffeine’s benefits without causing side effects was 38–400 mg per day. This equals roughly 0.3 to 4 cups of coffee daily, depending on the strength (19).
In one large review of 18 studies with over 450,000 people, there was a 9% reduction in type 2 diabetes risk for each cup of regular coffee consumed per day. The reduction for decaffeinated coffee was 6% for each cup consumed daily (23).
Green tea contains antioxidants known as catechins, which help reduce inflammation, a driver of the aging process and many diseases (26).
Bottom Line: Many studies have shown that coffee and tea have beneficial effects. This includes improved mood, increased mental and physical performance, enhanced metabolism and a reduced risk of several diseases.
4. Sugary Drinks Are Fattening
Sugar is more than just empty calories. In excess, it can lead to health problems and weight gain, especially when consumed in liquid form.
Sugar (sucrose) contains 50% glucose and 50% fructose, while high-fructose corn syrup contains 45% glucose and 55% fructose. Fructose has been linked to obesity and several chronic diseases, such as type 2 diabetes and heart disease (30).
In observational and controlled studies, sugar-sweetened beverages have shown a strong relationship to weight gain, including abdominal or visceral fat surrounding the liver and other organs (31, 32, 33, 34, 35).
In a controlled 10-week study, overweight people consuming 25% of calories in the form of fructose-sweetened beverages experienced a 14% gain in visceral fat (35).
Research suggests that calories consumed in liquid form don’t have the same appetite-suppressing effect as solid calories do. This leads to excess calories consumed throughout the day, which are then stored as fat (36, 37).
Bottom Line: Sugar-sweetened beverages have been shown to promote weight gain and unhealthy abdominal fat, which increases the risk of disease.
5. Extra Virgin Olive Oil Is Good for You
Extra virgin olive oil contains oleic acid, a type of monounsaturated fat that has been shown to lower triglycerides, raise levels of HDL (the good cholesterol) and increase the fullness-promoting gut hormone GLP-1 (39, 40).
In a large analysis of 32 studies looking at different types of fat, oleic acid from olive oil was the only fatty acid linked to reduced risk of heart disease (38).
Extra virgin olive oil also contains antioxidants called polyphenols. These can fight inflammation, lower LDL cholesterol and protect it from damage, improve the function of the cells lining your arteries and reduce blood pressure (41, 42, 43, 44).
Researchers who analyzed data from 5,800 people at an increased risk of heart disease found that the group treated with olive oil experienced a significant decrease in blood sugar levels and abdominal fat (45).
Bottom Line: Extra virgin olive oil contains oleic acid and antioxidants, both of which have been shown to reduce inflammation, lower cholesterol and improve other markers of heart health.
6. Cutting Carbs Improves Diabetes Management
Of the three macronutrients, carbs have by far the greatest impact on blood sugar. This is because they are broken down to sugar in the body.
In a study of 21 people with type 2 diabetes who followed a diet containing 20 grams of carbs or less per day, 81% of subjects were able to eliminate or significantly reduce insulin or diabetes medication after 16 weeks (51).
Although very low-carb diets have been proven extremely effective at lowering blood sugar, several studies have shown that a more modest carb reduction can also produce excellent results (52, 53, 54).
In one study, men with type 2 diabetes who consumed a high-fiber diet with 100 grams of digestible carbs per day for 5 weeks had a nearly 30% reduction in fasting blood sugar, on average (54).
Bottom Line: Low-carb diets containing 20–100 grams of digestible carbs per day have been shown to lower blood sugar levels. In some cases the participants can significantly reduce their diabetes medication.
7. A High Protein Intake Is Beneficial for Weight Loss
A high protein intake decreases levels of the “hunger hormone” ghrelin and increases the release of fullness hormones PYY and GLP-1. This leads to a natural reduction in your calorie intake (60, 61, 62).
In one controlled study, people who ate a diet containing 30% of their calories from protein ended up consuming 441 fewer calories per day without consciously restricting their intake (63).
Bottom Line: High-protein diets promote weight loss and maintenance by decreasing hunger, increasing feelings of fullness and boosting metabolism.
8. Nuts Are Healthy and Weight Loss Friendly
Nuts are delicious and provide many health benefits.
Several observational studies have shown a link between high nut consumption and a reduced risk of heart disease (67).
One study found that people who consumed nuts more than 4 times per week had a 37% lower risk of heart disease than people who ate nuts less often (68).
Almonds, pistachios, walnuts and Brazil nuts have been found to lower markers of inflammation, improve cholesterol levels and improve the function of the cells that line your arteries (69, 70, 71, 72, 73, 74, 75, 76).
Bottom Line: Nuts are anti-inflammatory, help protect heart health and are beneficial for weight control.
9. Ketogenic Diets Can Help Control Seizures
Epilepsy is a disease characterized by repeated seizures in the brain.
It is often treated with drugs that have strong side effects.
However, a very low-carb ketogenic diet has also shown promise in treating the disease.
Of the patients who do respond to the diet, results can be dramatic. In one study, children treated with a ketogenic diet for three months had a 75% decrease in seizures, on average (82).
The classic ketogenic diet limits protein intake to 10% of calories and carbohydrates to less than 5%.
In a controlled three-month study of 102 children, 30% of those who followed the modified Atkins diet had a 90% or greater reduction in seizures, while more than half had at least a 50% reduction (88).
Bottom Line: The classic ketogenic diet and modified Atkins diet have been shown to reduce seizures in many children with epilepsy.
10. Whole Grains Are Healthier Than Refined Grains
In one calorie-controlled study of overweight and obese adults, eating two portions of whole-grain oat cereal per day led to reductions in LDL cholesterol and belly fat (97).
Bottom Line: In most studies, whole grains have been shown to reduce inflammation, protect heart health and help with weight control. Refined grains have been linked to negative health effects.
11. Vegetables and Fruits Are Healthy
Eating vegetables and fruits on a regular basis is considered a very healthy practice.
Researchers who analyzed data from over 65,000 people found that those who ate at least seven servings of fruit or vegetables per day had a 42% lower risk of early death than those who ate less than one serving daily (105).
Certain vegetables and fruits may be especially protective against cancer. These include blueberries, vegetables high in beta-carotene such as spinach and carrots, and cruciferous vegetables such as broccoli and cauliflower (106, 107, 108).
Controlled studies in both healthy people and those with diabetes have found that increasing fruit and vegetable consumption boosts antioxidant levels in the blood and improves heart disease risk factors (109, 110, 111).
Bottom Line: Several large studies have found that eating fruits and vegetables is linked to a decreased risk of several diseases, including heart disease and cancer.
12. Omega-3 Fatty Acids Lower Triglycerides
Eating enough omega-3 fatty acids is very important.
They are good for the brain and have been shown to improve several risk factors, including blood triglycerides.
In one systematic review of 18 studies of more than 800 diabetics, taking 3-18 grams per day of fish oil led to a significant decrease in triglycerides (116).
Bottom Line: Omega-3 fatty acids have been shown to lower blood triglyceride levels in many studies, along with other benefits.
13. Calories Are Important, Although You May Not Need to Count Them
Although there are many factors that affect the rate and ease of weight loss, when people consume fewer calories than they need, they lose weight (122).
In fact, researchers who analyzed 37 studies of weight loss programs found that calorie counting was more likely to lead to weight loss than all other behavioral changes (124).
On the other hand, some people may find calorie counting stressful. In truth, counting calories may not be necessary if you eat in a way that helps you naturally consume fewer calories than you need.
Bottom Line: Reducing calorie intake is required for weight loss, but counting calories may not be appropriate for everyone.
14. Dietary Cholesterol and Whole Eggs Aren’t Bad For You
For several decades, dietary cholesterol was believed to raise blood cholesterol and increase the risk of heart disease.
However, studies show that when you eat more cholesterol, your body produces less.
In fact, eating eggs has been shown to improve some risk factors for heart disease, including raising HDL levels and promoting beneficial changes in the size and shape of LDL cholesterol (130, 131, 132, 133).
A small number of people, who are considered “hyperresponders” to cholesterol, have been found to experience a large increase in blood cholesterol levels in response to a high dietary cholesterol intake (134, 135, 136).
However, for most people, regularly eating eggs has been shown to be very healthy.
Importantly, you should eat the whole egg, including the yolk. That’s where almost all the nutrients are found.