By definition, a low fat diet is one that contains less than 30% of total calories from fat, while some ultra-low fat diets contain less than 15%. At a glance, cutting down on your dietary fat can seem like a good idea. But the science surrounding low fat diets is getting increasingly complicated.
The advice has changed over the years. Low fat diets were heavily promoted for decades and many were told to reduce their fat intake from foods such as butter, eggs, red meat and cheese to avoid cardiovascular disease, weight gain and high cholesterol levels. However, recent scientific studies suggest that the relationship between dietary fats and our health may not be as straight-forward.
Indeed, our bodies may need certain types of fat to function properly. To help cut through the confusion, we looked into current evidence surrounding low fat diets and talked to several nutrition experts.
Are there any benefits of a low fat diet?
When done right, low fat diets may improve the nutritional value of your foods. “They allow individuals more opportunities to incorporate complex carbohydrates that are rich in fiber into their diets,” says Ulrike Kuehl, registered dietitian at Lumen.
Kristen Smith, MS, RDN, LD, spokesperson for the Academy of Nutrition and Dietetics, agrees. “Typically when individuals follow a low fat diet, they will simultaneously increase their intake of fruit, vegetables and whole grain food sources, which can lead to a reduction in the risk of certain cancers, slow diabetes progression or prevent heart disease,” she says. “It may be particularly beneficial if you are at higher risk for heart disease or have a significant family history of heart disease.”
Kristen Smith is the bariatric surgery coordinator for Piedmont Healthcare. She is a fundraising co-chair for the Georgia Academy of Nutrition and Dietetics; a member of the Academy's Weight Management dietetic practice group; the American Society of Metabolic and Bariatric Society and the Obesity Action Coalition. She is a graduate of Oklahoma State University and earned a master's degree from New York University.
Low fat diets may also be beneficial for those who had their gallbladder removed, as indicated in the BMJ journal. Without this organ functioning properly, these individuals will not produce enough of the enzyme lipase which breaks down fat. As such, reducing their consumption of fat rich foods may significantly improve their digestion.
On the other hand, many experts don’t recommend cutting down your fat intake, pointing to the potential risk of malnutrition and associated health problems. At the same time, many researchers are debating whether cutting down on certain types of fat, as opposed to total fat, could be the best approach. Check our article on the unsaturated vs saturated fat to understand the differences between these two nutrient groups.
So what does science say about dietary fat?
Saturated fats
Saturated fats are found mostly in coconut oil and animal-based products like meat, eggs and dairy. Despite decades of research, scientists are still not sure what role these nutrients play in health and disease. Saturated fats used to be blamed for the rise in heart disease and other chronic conditions.
“Some research suggests saturated fat may promote inflammation and increase risk of heart disease because it can raise the ‘bad’ LDL cholesterol,” says Smith. Indeed, the American Heart Association continuously advises to cut down on saturated fat intake and eat more mono- and polyunsaturated fats instead.
However, recent studies have shown that it may not be as straight-forward and scientists are far from reaching an agreement on saturated fats. According to an article published in the British Medical Journal, replacing saturated fats with polyunsaturated fats can lower cholesterol levels, but it doesn’t translate to better heart health.
Trans fats
According to a review published in the Atherosclerosis journal, the type of dietary fat that should be avoided altogether is trans fats. Trans fats are usually the result of industrial hydrogenation processes aimed at changing the consistency of vegetable oils in highly processed foods. But you can also create them while cooking at home, particularly when frying with polyunsaturated oils like sunflower and corn oil. High temperatures can modify the structure of these fats, creating trans fats. They can be detrimental to health and increase the risk of coronary heart disease.
Cholesterol
Cholesterol is a fatty compound found in eggs, meat and dairy products. Low fat diets are naturally low in this nutrient. Our bodies need a certain amount of cholesterol to protect our nerves and produce new cells.
“While experts once believed dietary cholesterol would increase your risk of heart disease, more recent studies have shown consuming foods higher in cholesterol has little to no effect on blood cholesterol levels in most people,” says Smith. “This means there is no significant association between consuming foods higher in cholesterol and your risk of heart disease.”
However, researchers are far from agreeing on this issue. Although studies have shown that a high intake of dietary cholesterol may not always increase your blood cholesterol levels, it can still affect your cardiovascular health.
According to a meta-analysis published in the Circulation journal, dietary cholesterol and egg consumption may be linked to an increased risk of dying from heart problems. What’s more, scientists from the Nutrients journal suggest that high cholesterol intake may fuel inflammation within your immune system, which can make you more prone to infections and autoimmune diseases.
Cancer
Low fat diets may be potentially beneficial for cancer prevention. According to a review published in the International Journal of Molecular Sciences, high fat intake can significantly impact gut health and increase inflammation levels, two risk factors for many types of cancer. However, the composition of fat may be more important to the tumor development than the total fat content. Also, it needs to be stressed that there is no solid evidence that low fat diets can effectively treat existing cancers.
Low fat diet: Implications & risks
Malnutrition
Fat is vital for our health, and its main role is to provide energy for our bodies. Cutting down on fat may lead to fatigue – and some individuals may compensate with eating more carbohydrates. “When following a low fat diet, it can cause the intake of carbs to be higher, and individuals have more of an opportunity to consume less healthy carb-rich foods,” explains Kuehl. “They may also eat more low-fat highly-processed foods.”
Smith also stresses that fats are not created equal. “Some fats such as mono- and poly-unsaturated fats can actually offer many health benefits, including reducing your risk of heart disease,” she says. “Foods such as salmon, avocado and nuts are examples of foods containing a substantial amount of fat, but yet still offer heart healthy benefits”
For example, low fat diets may be short of essential omega 3 fatty acids. Omega-3 fats have been shown to be essential for the proper functioning of our cardiovascular, immune and nervous systems.
Low fat diets may also lead to certain deficiencies. “Following a low fat diet can put people at risk of low intake of the fat-soluble vitamins A, D, E and K,” says Caroline Hind, nutritional therapist for Vitaminology. “These vitamins are often present in foods that contain fat and they need to be eaten with fat in order to be absorbed properly in the body.”
Long-term weight loss
Low fat diets are commonly used for weight loss, but research suggests it may not be the best approach. Multiple studies have shown that despite providing good initial results, low fat diets may not be suitable long-term. That’s because they may lead to problems with hunger management. Low fat diets are not satiating and may lead to the overconsumption of carbohydrates.
Mental health
Emerging evidence suggests that low fat diets may have a negative impact on our mental wellbeing. According to a review published in the Global Health Journal, polyunsaturated fatty acids play a fundamental role in the development, functioning, and aging of the brain. Not eating enough omega-3s can lead to an increased risk of various psychiatric disorders, including depression, dementia, autism and ADHD.
Skin
Fat is a crucial element of skin cell membranes – it maintains the skin barrier, locks in moisture and protects the skin from injury. According to a review in the International Journal of Cancer, omega-3s and other essential fatty acids may also protect us from sunburn and skin cancer. Since we shed thousands of skin cells on a daily basis, our bodies need sufficient amounts of fat to keep our largest organ in peak condition. Therefore, low fat diets can lead to dry and flaky skin that’s more sensitive to UV radiation and inflammation.
Reproductive health
Fat is an essential component of many important steroid hormones in our bodies. Low fat diets can especially affect the production of sex hormones like estrogen and testosterone. Low levels of reproductive hormones may lead to fertility problems, irregular menstrual cycles, low libido and mood swings.
How much fat should you eat?
According to USDA dietary guidelines, there is no upper limit to the amount of total fat you can consume. Many high-fat, low-carb diets, such as keto and Paleo, are considered safe for most healthy adults. Based on the dietary reference intake (DRI) values, adults should consume between 20% to 35% of their total calories from fat. Assuming that you need approximately 2000 calories a day, that will come down to around 44-77 g of dietary fat per day. Most of your calories should come from monounsaturated and polyunsaturated fats: 15- 20% and 5-10%, respectively. No more than 10% of your calories should come from saturated fats, while trans fats should be avoided altogether.
Low fat diets: What to watch out for
Many different foods are branded as ‘low fat’ or ‘fat free’. Some of them are naturally low in this macronutrient, like chicken breasts, white fish, egg whites or whole grain bread. However, the vast majority of ‘low fat’ foods have been modified to contain less fat. These include various low fat dairy products, breakfast cereals, salad dressings, peanut butters, muffins, cereal bars and sandwich spreads. Because they’re marketed as ‘healthier alternatives’, you may be tempted to include these foods in your low fat diet. But make sure to inspect their labels first. More often than not, ‘low fat’ and ‘fat free’ products contain a range of unhealthy ingredients, such as hidden sugars and artificial sweeteners.
Sugar is a common filler in ‘low fat’ products. Starchy carbohydrates are another popular fat substitute. The American Heart Association recommends that women should eat no more than 25 g of added sugar a day (six teaspoons), while men should stick to the limit of 36 g of added sugar a day (nine teaspoons). So if you eat ‘low fat’ foods regularly, you may end up consuming excessive amounts of simple carbohydrates.
“When meals and snacks are predominantly made up of starchy and sugary foods, we are at increased risk of metabolic disturbances such as weight gain and type 2 diabetes,” says Hind. “My recommendation is to reduce processed fats such as those in fried convenience foods, but not to worry about the fats in whole foods such as avocado, eggs and olives.”
And if you’re not sure whether you’re following the right diet, it’s always good to consult a professional. “Working with a registered dietitian nutritionist can be helpful,” says Smith. “They can help you put together balanced meal options that will meet your health needs and work with your current lifestyle.”
Additional resources
- American Society for Clinical Nutrition: Protein, body weight, and cardiovascular health
- American Journal of Epidemiology: Effects of Low-Carbohydrate Diets Versus Low-Fat Diets on Metabolic Risk Factors
- National Center for Biotechnology Information: Long-term effects of a ketogenic diet in obese patients
