The American Heart Association (AHA) recently published a review of current knowledge on the association between dietary fats and cardiovascular disease. By taking into consideration the entirety of the available scientific evidence, the committee concluded that a lower intake in saturated fat and replacing it with unsaturated fat represents the optimal combination to reduce the incidence of heart disease in the population, especially if it is accompanied by a transition toward an overall healthy diet, such as the Mediterranean diet.
The positive impact of substituting saturated fat with unsaturated fat can mainly by explained by the opposite effects of these two types of fat on the LDL cholesterol level, a well-established risk factor for cardiovascular disease. Whereas saturated fat is associated with an increase of this cholesterol, and thus an increase in the risk of cardiovascular events, unsaturated fat leads to a decrease in LDL cholesterol levels in the blood and is associated with a significant decrease in mortality. Since animal-based protein sources (meat, dairy products, eggs) are the main sources of saturated fat in diets, whereas plant-based fats are mainly unsaturated, the mere act of reducing consumption of animal products while simultaneously increasing the consumption of plant-based foods is a very easy way to improve the quality of dietary fats, and thus reduce the risk of heart disease. In fact, it is interesting to note that several regions of the world known for their low incidence of cardiovascular disease (Okinawa, Japan; Ikaria, Greece; Sardinia; and the Tsimané people of the Amazon) all share one commonality: a diet high in plant-based foods with a low intake of animal protein and saturated fat.
Plant-based saturated fat
Whereas almost all plant-based fats mainly contain unsaturated fat, there is nevertheless one notable exception: tropical palm and coconut oils (see the Table). Indeed, palm oil (extracted from the fruit pulp) and palm kernel oil (derived from the kernels) contain very high levels of saturated fat (50% for palm oil and 82% for palm kernel oil), which gives them a semi-solid texture at room temperature. This property is used in the food industry to improve the texture of cookies, cakes and other products, and the high level of saturated fat also ensures that these oils are much more resistant to oxidation and considerably improves the shelf life of these foods. However, like all sources of saturated fat, these oils increase blood cholesterol levels and thus are not recommended for cardiovascular health. Not to mention the devastating environmental impact of the intensive cultivation of oil palm, in particular in Indonesia: almost two million hectares of tropical forest are destroyed every year for this crop, a deforestation that has disastrous environmental consequences and threatens animals such as tigers and orangutans from Sumatra and Borneo with extinction.
Table. Proportion of saturated, monounsaturated and polyunsaturated fat in different animal and plant-based fats.
|Source of fat||Saturated fat|
|Palm kernel oil||82||11||2
Coconut oil: saturated fat with positive effects?
Coconut oil is another plant-based source that contains a very high proportion of saturated fat (82%), but that, curiously, has gained a good reputation over the years. In fact, a recent survey reported that 72% of Americans consider coconut oil a “healthy” food! Two main characteristics of coconut oil, frequently mentioned in mainstream press, explain this popularity:
1) Population studies. Epidemiological studies conducted among populations that consume large quantities of coconut, such as the inhabitants of Polynesian islands like Tokelau or those of the Melanesian island Kitava, revealed a low incidence of heart disease, despite a high intake of saturated fat from this fruit. It should be noted, however, that it is the coconut meat, very high in fibre, that is consumed by these populations, so the lack of effect on cardiovascular disease cannot be extrapolated to that associated with adding purified coconut oil to Western diets, which contain a large proportion of processed foods.
2) Impact on cholesterol. The saturated fat in coconut oil has shorter chains than that found in palm oil or in butter, and, in theory, has less harmful effects on cholesterol levels. About half of saturated fat contained in coconut oil is in the form of lauric acid (12 carbon atoms), and studies show that the effect of this fatty acid on LDL cholesterol is half that of palmitic acid (16 carbon atoms). In practice, however, a systematic review of the studies conducted to date indicates that coconut oil increases LDL cholesterol levels in a similar way to other sources of saturated fat (butter, palm oil) and in a more significant way than unsaturated fat, such as olive oil for example.
Overall, these observations suggest that coconut oil is a source of saturated fat like any other, and that it should be used sparingly to prevent an increase in the risk of heart disease. For everyday cooking, virgin olive oil is a much better choice because of its very well documented positive effects on cardiovascular health. Among other plant-based oils, the use of canola oil is recommended, as it contains the highest proportion of omega-3 polyunsaturated fats, known for their anti-inflammatory effects.
The excessive accumulation of body fat, particularly when concentrated in the abdomen, is an important risk factor for several diseases, including heart disease, type 2 diabetes, dementia as well as several types of cancer. Consequently, for people who are overweight or obese, weight loss is a very important way to reduce the incidence and progression of several of these diseases.
Many studies show that weight loss is indeed associated with a significant improvement of several aspects of the metabolism. For example, an American study showed that among overweight individuals with diabetes, a 5-10% loss of body weight was associated with a notable improvement of several risk factors for heart disease (glycemia, blood pressure, triglycerides, HDL cholesterol) after one year. These positive effects are even more pronounced when weight loss is more significant, in particular with regard to sugar metabolism, but the key takeaway is that weight loss, even when relatively modest, has a very positive impact on health.
Unfortunately, losing weight is not a “small” matter, since it entails significantly reducing calorie intake for long periods. However, the results of the CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) study show that it is possible: in this study, conducted over two years, participants successfully reduced their calorie intake by 12%, which translated into a 10% weight loss and a significant improvement of several cardiometabolic risk factors. However, this decrease in calorie intake was well below what researchers wanted (25%), even though participants were closely monitored and could ask for advice from several specialists in the research team. Significantly reducing food consumption, namely by 500 to 600 calories daily, thus represents a difficult objective to achieve for most people, which explains the well-documented difficulty of adhering, in the long term, to popular weight loss diets developed over the last few years. Generally, these diets are associated with relatively significant short-term weight loss, but it is very difficult to maintain this loss in the longer term and the majority of people regain the lost pounds (and sometimes even more) after a certain time. When these diets are repeatedly attempted, they cause what is known as the “yo-yo” effect, which is not only discouraging but can also be harmful to health: in fact, a recent study showed that in patients with a history of cardiovascular events, frequent body-weight fluctuations were associated with a marked increase in the risk of myocardial infarction (117%), stroke (136%), diabetes (78%), and premature death (124%).
Strict but brief restriction
To overcome these limitations, more and more researchers have focused on fasting as a way to take advantage of the benefits associated with caloric restriction. Instead of consistently reducing the number of calories consumed every day, which seems virtually impossible for the majority of people, this approach involves alternating periods of normal calorie intake with more or less prolonged fasting periods. What we refer to as “intermittent fasting”, for example, consists of fasting or drastically reducing calorie intake (500 calories a day) intermittently, for example, 1 or 2 days a week. These fasting periods can be consecutive, as in the 5:2 diet (5 days of normal diet followed by two days of fasting), or alternating (one out of two days, for example). In both cases, studies show that intermittent fasting is associated with weight loss and an improvement of several cardiometabolic markers, similar to the results obtained following continuous caloric restriction, and could therefore present an interesting alternative.
Nevertheless, an inherent limit to this type of strict fasting is that it remains very difficult for many people to completely deprive themselves of food for 2-3 days. Not to mention that the complete elimination of calories can lead to severe complications in some people, in particular in elderly or frail subjects.
It is in this context that Dr. Valter Longo’s team (University of South California) came up with the idea of developing a diet that reproduces the positive effects of fasting on the body, but without completely forgoing food. Their research conducted on mice showed that a less strict caloric restriction (calories reduced by half), achieved through a plant-based diet high in polyunsaturated fats but low in protein and carbohydrates, could mimic the effects of very strict fasting on several cardiometabolic risk factors and was associated with a significant improvement on health (fewer cancers, reduction in bone-density loss, improvement of cognitive performance) as well as of the life expectancy of the animals. Referred to as the “fasting mimicking diet” (FMD), this new type of caloric restriction could thus represent a new approach to not only lose weight but also improve health in general.
This strategy’s potential is clearly illustrated by the results of a phase 2 clinical study recently published in Science Translational Medicine. The 100 study participants were divided into a control group that followed their usual diet, and a study group that were prescribed the FMD for 5 consecutive days every month, for a period of three months. Afterward, the groups were switched, meaning that the participants from the first control group tested the FMD, whereas the volunteers in the study group reverted to their usually dietary habits.
The results obtained are extremely interesting. One week following the end of the third caloric restriction cycle using the FMD, participants had lost on average 3 kilos (6.6 lb.), had a smaller waistline (3 cm), and showed an improvement in their blood pressure compared to the control group (- 4 mm Hg). Positive effects of caloric restriction on fasting glucose, the lipid profile (triglycerides, cholesterol), inflammatory protein levels (C-reactive protein), and certain growth factors such as IGF-1 (implicated in the development of cancer) were also observed, in particular in individuals who presented anomalies in these markers at the start of the study. For example, the blood sugar level of participants who were prediabetic at the beginning of the study returned to normal after the intervention.
Caloric restriction using the FMD is still at the experimental stage and further research is necessary to better evaluate its effects in the longer term. In the meantime, one thing is certain: most chronic diseases currently affecting the population are a consequence of the overconsumption of food, and there are only advantages to eating less, even if only a few days a month.