In the past, dietary fats had a bad reputation of being harmful for health and of being responsible for weight gain. New research, however, demonstrates that certain healthy fats are necessary to promote good health.
In addition, important studies like the Nurses’ Health Study and the Health Professionals Follow-up Study did not find any correlation between the overall percentage of calories from fat and health outcomes. What really matters is the quality of fats rather than their quantity.
Unsaturated healthy fats and Omega 3 fatty acids benefits
The good healthy fats are unsaturated fats. These fats, which are liquid at room temperature, can improve blood cholesterol levels, reduce inflammation, stabilize heart rhythms, and bring a number of other health benefits.
Unsaturated fats are present in large quantities in foods from plants such as vegetable oils (like olive oil), nuts, seeds, and fish.
There are two types of unsaturated fats: monounsaturated and polyunsaturated.
Monounsaturated fats are present in abundance in olive, peanut, and canola oils, avocados, nuts such as almonds, hazelnuts, and pecans, seeds like pumpkin and sesame seeds.
Polyunsaturated fats can be found in sunflower, corn, soybean, and flaxseed oils, walnuts, flax seeds, fish and canola oil, which is a good source of both monounsaturated and polyunsaturated fat.
Omega-3 are particular polyunsaturated fats that are very important to promote good health. Our body is not able to manufacture Omega-3 fats, for this reason we must eat them from food. Omega-3 fats decrease the risk of premature death in older adults, according to a study by HSPH faculty. These types of fats can be found in great quantities in fish and plant food such as flax seeds, walnuts, and canola or soybean oil.
Alpha Linoleic Acic (ALA) is the omega 3 fatty acid that is normally found in plant foods such as nuts and fatty seeds like linseed. Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) are the omega 3 fatty acids that are normally found in fish, that’s why these are called “marine” omega 3.
The American Heart Association recommends that 8-10% of daily calories intake should come from polyunsaturated fats, and there is evidence that eating up to 15% of total calories of polyunsaturated fat in place of saturated fat can lower heart disease risk.
Replacing some carbohydrates with unsaturated fats can also be a good idea. In clinical trials where unsaturated fats were eaten in place of carbohydrates, harmful levels of LDL decreased and levels of protective HDL increased. This is of course only directional, it does not mean that you should replace all carbs with unsaturated fats; this rather means that most people would benefit by reducing the quantity of carbohydrates in favor of eating more unsaturated fats. A recent study indicates that replacing a carbohydrate-rich diet with one rich in unsaturated fat, predominantly monounsaturated fats, lowers blood pressure, improves lipid levels, and reduces the estimated cardiovascular risk.
Saturated fats
In contrast to unsaturated fats, saturated fats have a negative impact on health and should be consumed in moderation. Foods that are rich in saturated fats include red meat, meat products such as sausage, bacon, beef, hamburgers; butter, cheese, ice cream, fat dairy products in general, cookies and other grain-based desserts, and many fast-food dishes. Saturated fats are also present in large quantities in some plant-based foods like coconut, coconut oil, palm oil and palm kernel oil.
Normally, all foods containing fat have a certain percentage of saturated fat. This includes healthy foods like chicken and nuts; however, the percentage of saturated fats in these cases are much lower than in less healthy foods like beef and cheese.
Historically, research indicated that saturated fat was harmful, recently, however, new studies found that diets rich in saturated fat do not raise the risk of heart disease. In order to bring some clarity, the Harvard School of Public Health looked into the question “Saturated or not: Does type of fat matter?“ and the outcome of their analysis is that cutting back on saturated fat can be good for health if these are replaced with good fats, in particular polyunsaturated fats.
The Dietary Guidelines for Americans recommends eating less than 10% of daily calories from saturated fat and the American Heart Association recommends less than 7%.
It is important to pay attention to what saturated fats are replaced with. In fact, in industrially produced foods, manufacturers often replace saturated fats with sugar, refined grains, or other starches that affect blood sugar and insulin levels, potentially resulting in weight gain and disease. When saturated fats are reduced and replaced with refined carbohydrates, “bad” LDL cholesterol go down, but also the “good” HDL cholesterol go down and triglycerides increase, ultimately not bringing any benefits for health.
The best strategy is to reduce consumption of foods that are high in saturated fats like red meat and butter, and replace them with foods that are high in unsaturated fats like fish, beans, nuts, and healthy oils.
Trans fats
The worst type of fats are the trans fats. Eating trans fats also in small quantities increases disease risk. This type of fats is present mainly in processed foods in the form of partially hydrogenated oil. In recent years trans fats have been eliminated from most processed foods but it’s still a very good idea to read ingredients labels and avoid eating food that contains them. Trans fats are made through a process called hydrogenation that consists in heating liquid vegetable oils in the presence of hydrogen gas and a catalyst to obtain partially hydrogenating vegetable oils. The quality that makes these oils interesting to the food industry is that these are more stable and less likely to become rancid. In addition, hydrogenation makes these oils solid at room temperature making them suitable to be used as margarine or shortening. In addition, these partially hydrogenated oils can be heated repeatedly without losing their qualities and this makes them ideal for frying in fast food restaurants. Trans fats are also very suitable for the food industry to be used in baked and snack foods.
Trans fats, however, are not only present in partially hydrogenated oils but also naturally in small amounts in beef and dairy fat.
Trans fats are the worst type of fat for our health and are harmful even in small amounts. In fact, even just eating additional 2% of daily calories from trans fat results in an increase of 23% in the risk of coronary heart disease. They also raise bad LDL and lower good HDL (see the following section to learn more about LDL and HDL), contribute to insulin resistance and create inflammation that is connected to heart disease, stroke, diabetes and other chronic conditions.
Triglycerides and Cholesterol
Triglycerides are a type of fat that makes most of the fat you eat and that travels through the bloodstream. When you eat, the body converts any calories in excess into triglycerides that are stored in your fat cells. Later, hormones release triglycerides for energy between meals. They are the body’s main vehicle for transporting fats to cells, therefore they play an important role for health. However, high levels of triglycerides can be unhealthy.
Cholesterol is a lipid that is used by the body to make estrogen, testosterone, vitamin D, and other important compounds. Cholesterol is present in certain foods, however for most people dietary intake of cholesterol is not so determining for health as once believed. Although it remains important to limit the amount of cholesterol intake from food, what really impacts blood cholesterol levels is the mix of fats and carbohydrates you eat, not the amount of cholesterol you eat from food.
In particular, it’s the presence of the bad LDL cholesterol in the bloodstream that impacts our health. To explain why this is the case, we should understand how fat is transported from food to the bloodstream. Fat and cholesterol cannot dissolve in water or blood, so our body packages them into tiny protein-covered particles called lipoproteins as they can carry a lot of fat and mix well in the bloodstream.
The most important lipoproteins are low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides.
Low-density lipoproteins (LDL) transport cholesterol from the liver to body cells that extract fat and cholesterol from them. When there is too much LDL in the bloodstream, these particles can deposit on the coronary and other arteries and create plaques that can restrict blood flow. When these plaques break apart, they can cause a heart attack or a stroke. For these reasons, LDL is called bad cholesterol, as it has a negative effect on health.
High-density lipoproteins (HDL) wipe cholesterol from the bloodstream, from LDL, and from artery walls and transport it to the liver for disposal. That’s why HDL cholesterol is a good one, as it has a beneficial effect on health.
Having lower LDL and higher HDL maximizes the chances of preventing heart disease and other chronic conditions.
It’s established that high blood cholesterol levels strongly increase risk for heart disease, however the relationship between dietary cholesterol and cholesterol in the bloodstream is controversial.
Recent studies suggest that cholesterol in food matters, but not so much. What really matters is the type of fat and the types and amount of carbohydrates eaten from food.
For most people, the amount of cholesterol eaten from food has a modest impact on the amount of cholesterol in the bloodstream. However, for some “responders” people dietary cholesterol has a greater impact on bloodstream cholesterol. As of today, unfortunately, there is no clear way to identify these “responders” people apart from a trial and error approach.
For example, a Harvard study on more than 80,000 female nurses found that consuming about an egg a day was not associated with higher risk of heart disease. However, people who have heart disease or diabetes should monitor egg consumption.
Evidence-based takeaway on healthy fats
The types of fats in your diet can affect your health by promoting good health, helping to prevent and fight various diseases.
The good polyunsaturated fats can help prevent type 2 diabetes, whereas trans fats promote it. For people already affected by diabetes, eating omega-3 fats from fish and foods rich in unsaturated fats can help protect against fatal heart disease.
Contrary to what science suggested in the past, recent research indicates that there is no clear evidence linking consumption of any specific type of fats with cancer incidence, with the exception of the cases that follow.
Some studies provide evidence that animal fat intake in young women is linked to higher risk of breast cancer. Women who ate diets rich in animal fats had 40 to 50% higher risk of breast cancer, compared to women who ate diets with the lower percentage of animal fats. In addition, vegetable fat was not associated to risk of breast cancer, suggesting that red meat and high-fat dairy products may contain other factors, such as hormones, that increase risk of breast cancer. Other studies provide findings of lower breast cancer risk in women with high consumption of monounsaturated fats, mainly from olive oil.
Science does not currently provide evidence of impact of dietary fat consumption with colon cancer. However, there is strong evidence that consumption of processed meat and red meat increase colon cancer risk.
Finally, Harvard researchers found evidence that consumption of trans fats is associated with risk for non-Hodgkin’s lymphoma.
When it comes to fats, in order to promote good health, you should prioritize foods that deliver healthy fats. This means avoiding trans fats, limiting saturated fats and adding in foods that deliver unsaturated fats, including omega-3 fats. In simpler words, limit red meat, full-fat milk, and dairy products, and avoid processed meat, and replace most of the saturated fats with health unsaturated fats, including omega-3, such as olive oil, nuts, seeds and fatty fish.
