Coconut oil has gained popularity as a health food, with some proponents claiming it aids in weight loss. However, scientific evidence presents a more nuanced picture. This article examines the existing research to determine the potential effects of coconut oil on weight loss and overall health.
Conflicting Evidence: A Mouse Study Raises Concerns
A recent study has cast doubt on the health benefits of coconut oil. The study found that low doses of coconut oil added to the diet of mice for eight weeks led to alterations in their metabolism that contributed to the development of obesity and related co-morbidities. Specifically, the coconut oil disturbed the mice’s ability to properly use leptin and insulin, two hormones important for regulating energy expenditure, hunger, and how the body handles fats and sugars.
The researchers found that the coconut oil produced stress in the endoplasmic reticulum. This is an area of a cell, where proteins are made and processed.
These findings support the hypothesis that a diet high in saturated fatty acids can lead to leptin resistance. At the same time as leptin resistance is developing, the body’s fat storage tissue, known as white adipose tissue, also becomes less responsive to leptin.
The study builds upon previous research in which the authors observed that coconut oil produced a central and peripheral inflammatory response, weight gain, a higher percentage of fat, reduced energy expenditure, and anxious behavior in mice, suggesting a systemic imbalance.
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The daily coconut oil doses were calorically similar to what would equal about 13 grams of saturated fat or 5% of the saturated fat calories for a healthy human adult.
Dr. Taylor Wallace, a nutrition scientist, commented on the study's findings, stating, "The study proposes that coconut oil could make it harder for the body to properly respond to important hormones that manage hunger and energy use, at least in mice. This could potentially contribute to problems like obesity and resistance to insulin, which is a key issue in diabetes." He further explained that "the coconut oil seemed to mess with the normal signaling pathways in the brain and other tissues that these hormones use to communicate their messages."
However, it's crucial to interpret these findings with caution. Dr. Wallace listed some of the factors that may give pause, including biological differences, dose differences, mice’s tightly controlled experimental environments that lack the variables found in a human study, genetic uniformity, rodents’ simpler systems, rodent interspecies differences, and ethical concerns.
Dr. Wallace emphasized that "while rodent studies can provide invaluable insights and guide further research, they are usually considered preliminary. They can highlight potential areas of concern or benefit that deserve further study in humans.” In fact, he noted that in a systematic review, only 37% of animal studies were replicated in humans, and 20% of them showed contradictory results.
Registered dietitian Kristin Kirkpatrick also noted that the relevance of the study’s findings to humans is not completely clear. “Impossible to say with certainty, however, studies find that mice and humans share similar genetics, so it’s a great first start.” Kirkpatrick cited a 2022 study that “concluded that more human studies assessing coconut oil are needed, but that some things to consider are the amount consumed and the processing of the oil itself.”
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Examining Human Studies: A Systematic Review
Despite the concerning mouse study, some human studies have shown potential benefits of coconut oil for weight management. A systematic review of nine studies examined the impact of coconut oil on obesity parameters. When compared to other oils and fats, coconut oil substantially decreased BW (N.=546), Body Mass Index (BMI) (N.=551), and percentage of fat mass (FM%) (N.=491) by 0.75 kg (P=0.04), 0.28 kg/m2 (P=0.03), and 0.35% (P=0.008), respectively. The period of coconut oil intake varied from four to twelve weeks, apart from one long-term trial where coconut oil was consumed for two years. Results indicate a small statistically significant reduction in BW, BMI, and FM% in the coconut oil group.
Analyzing Individual Studies: Mixed Results
Several individual studies have explored the effects of coconut oil on various health markers. Here's a summary of some key findings:
- Metabolism and Energy Expenditure: Some studies suggest that coconut oil, specifically its medium-chain triglyceride (MCT) content, may increase metabolism. Twelve females without overweight followed an MCT diet for 14 days. They consumed butter and coconut oil as their main sources of fat. For another 14 days, they followed a long-chain-triglyceride (LCT) diet, consuming beef tallow as their main source of fat. After 7 days, the resting metabolic rate and the calories burned after meals were significantly higher on the MCT diet compared with the LCT diet. After 14 days, the difference between the diets was no longer statistically significant.
- Fat Oxidation: Twelve females without overweight consumed a mixed diet supplemented with either butter and coconut oil (MCT diet) or beef tallow (LCT diet) for 6 days. For 8 days, both groups consumed LCTs, so that the researchers could assess fat burning. By day 14, the MCT group burned more body fat than the LCT group. Resting metabolic rate was significantly higher on day 7 in the MCT group compared with the LCT group, but the difference was no longer significant by day 14.
- Visceral Adiposity: Twenty people with either overweight or obesity consumed 10 mL of virgin coconut oil three times per day before meals for 4 weeks, or a total of 30 mL (2 tablespoons) per day. Otherwise, they followed their usual diets and exercise routines. After 4 weeks, the males had lost an average of 1.0 inches (2.61 cm) and females an average of 1.2 inches (3.00 cm) from around the waist. The average weight loss was 0.5 pounds (0.23 kg) overall and 1.2 pounds (0.54 kg) in males.
- Abdominal Obesity: Forty females with abdominal obesity took either 10 mL of soybean oil or coconut oil at each meal, three times per day for 12 weeks. This amounted to 30 mL (2 tablespoons) of oil per day. The researchers also asked them to follow a low-calorie diet and walk 50 minutes daily. Both groups lost about 2.2 pounds (1 kg). However, the coconut oil group had a 0.55-inch (1.4-cm) decrease in waist circumference, whereas the soybean oil group had a slight increase. The coconut oil group also had an increase in high-density lipoprotein (HDL) or “good” cholesterol, and a 35% decrease in C-reactive protein (CRP), a marker of inflammation. Additionally, the soybean oil group had an increase in low-density lipoprotein (LDL) or “bad” cholesterol, a decrease in HDL (good) cholesterol, and a 14% decrease in CRP.
- Lipid Profile and Antioxidant Enzymes: This study involved 70 males with type 2 diabetes and 70 males without diabetes. Researchers divided the participants into groups based on their use of coconut oil versus sunflower oil for cooking over a 6-year period. There were no significant differences in any values between the coconut oil and sunflower oil groups. Those with diabetes had higher markers of oxidative stress and heart disease risk than those without diabetes, regardless of oil type.
Coconut Oil and Cholesterol Levels
Several studies have investigated the effects of coconut oil on cholesterol levels. One study involving twenty-eight people with high cholesterol followed three diets containing coconut oil, butter, or safflower oil as the main fat source for 6 weeks each. Coconut oil and butter increased HDL significantly more than safflower oil in females, but not in males. Butter raised total cholesterol more than coconut oil or safflower oil.
Another study involving nineteen males with normal cholesterol levels consumed lunch and dinner containing three different fats for three sequential trial periods. Those who followed the coconut oil diet had higher levels of total, HDL (good), and LDL (bad) cholesterol than those who consumed the beef fat and safflower oil diets. However, their triglyceride levels rose less than those who consumed beef fat.
In a study involving twenty-five females consumed three diets: a high fat, coconut oil-based diet, a low fat, coconut oil diet, a diet based on highly unsaturated fatty acids (HUFA). In the high fat, coconut oil-based diet group, HDL (good) and LDL (bad) cholesterol levels rose more than in the other groups. In the low fat, coconut oil-based diet group, LDL (bad) cholesterol levels rose more, compared with HDL (good) levels. In the other groups, LDL (bad) cholesterol fell in comparison with HDL (good).
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Other Potential Benefits of Coconut Oil
Beyond weight management and cholesterol, research suggests coconut oil may offer other health benefits:
- Dental Health: The practice of oil pulling with coconut oil may reduce the bacteria responsible for plaque. In addition, it significantly improved gingivitis in the study involving teenagers.
- Quality of Life in Breast Cancer Patients: Adding a small amount of coconut oil to the diet while undergoing chemotherapy for breast cancer may improve a person’s quality of life at this time.
Considerations and Cautions
While some studies suggest potential benefits, it's essential to consider the limitations and potential drawbacks of coconut oil consumption:
- High Calorie Content: Each tablespoon of coconut oil provides 130 calories. The extra calorie intake might outweigh the benefits to the metabolic rate.
- Individual Variability: Responses to dietary fats can vary widely between individuals. For many, consuming too much of any type of fat can lead to weight gain and related health problems.
- Saturated Fat Content: Among common dietary fat sources, coconut oil has the highest percentage of saturated fats. The American Heart Association’s scientific advisory statement agrees on the greater health value of unsaturated fats, noting that coconut oil has been seen to increase LDL (“bad cholesterol”) levels. For people with an existing heart condition or who are at risk of one, the organization suggests consuming no more than 6% of a day’s calories from saturated fat.