Can Extremely Fat-Restricted or High-Fat Diets be Effective — and Safe — for Weight Loss?

AndreyPopov/ iStock / Getty Images Plus
AndreyPopov/ iStock / Getty Images Plus

For decades, dietary fat has been under the microscope as a nutrient that may heal or hinder health. Although the Institute of Medicine recommends an acceptable macronutrient distribution range, or AMDR, of 20 percent to 35 percent of total calories from fat per day, some health experts advise consuming higher levels and others recommend much lower amounts.

Two diets with opposing beliefs on fat are the oil-free, plant-based diet and the ketogenic diet. As its name implies, the oil-free, plant-based diet advocates an extremely fat-restricted eating pattern to stop, reverse or prevent cardiovascular disease. This diet does not allow any oils — even olive and canola, which are high in monounsaturated fats that some studies have shown deliver heart-health benefits. The ketogenic diet advocates moderate amounts of protein, very low amounts of carbohydrate and high amounts of fat — even saturated fats, which some research has shown to be detrimental to heart health. This diet causes the liver to generate ketone bodies for energy instead of glucose.

Advocates of low-fat diets are using the oil-free approach as a means to control calories from fat by getting calories primarily from plant foods; low-carb followers tend to jump on the ketogenic diet and strictly limit calories from carbohydrates while boosting fats to trim their waistlines. But what do we know about the safety, efficacy and implications of these two diets?

Going Oil-Free

The premise of the oil-free diet is that all dietary fats — even unsaturated oils, such as olive and canola, as well as avocado and nuts — can lead to heart disease. One of the cardiologists who spearheaded this plant-based, very low-fat approach was Caldwell B. Esselstyn Jr., MD, at the Cleveland Clinic. In 1985, Esselstyn began putting his cardiac patients on plant-based diets consisting of fruits, vegetables, whole grains and legumes, and excluding all added fats, including oils, dairy, meat, poultry, fish and nuts.

Walnuts are the one exception; they are allowed in small amounts because of their omega-3 fatty acid content.

Predicated on halting and reversing heart disease, the oil-free, plant-based diet has shown promise in some studies. A 2014 study authored by Esselstyn and colleagues in the Journal of Family Practice placed 198 patients with CVD on an oil-free, plant-based diet with intensive nutrition counseling in plant nutrition. After 3.7 years, Esselstyn and colleagues found that 177 participants (89 percent) who adhered strictly to the plant-based approach had a lower rate of subsequent cardiac events. Compliance in this study was high, but this may not be the case in the general population, for which meat, fats and oils are a large part of everyday eating patterns.

A positive aspect of the oil-free, plant-based diet is that it treats a primary cause of CVD — poor dietary habits consistent with the Western diet, which is high in animal fats from foods such as butter, beef, cheese and ice cream. However, it eliminates the so-called “heart-healthy” fats, such as olive and canola oils, nuts and sometimes avocado. The scientific rationale for eliminating all oils from the diet is that all oils are very low in nutritive value with no fiber or minerals and, therefore, are entirely fat calories.

Proponents of the oil-free approach also believe all oils, whether they contain mostly unsaturated or saturated fat, are harmful to the endothelium (the inner lining of the artery) and that this damaging effect is the precursor to disease. Thus, regardless of the type of oil, it’s on the avoid list.

Since this diet is vegan, it requires supplementation for vitamin B12, an essential nutrient found primarily in animal products. For an omega-3 fat boost, this regimen allows 1 to 2 tablespoons of flaxseed meal or chia seeds. Some health experts may be concerned about the absorption of fat-soluble vitamins — A, D, E and K, as well carotenoids — on this extremely low-fat diet. Eating fewer than 20 percent of total calories from fat per day falls below the AMDR, which can create safety concerns for vitamin and antioxidant absorption rates. Without adequate fat in the diet, the risk for nutrient deficiencies rises.

In fact, some researchers dispute the effectiveness of the oil-free diet approach. A 2002 research review conducted by Harvard professors Frank Hu, PhD, and Walter Willet, PhD, in the Journal of the American Medical Association examined 147 studies on the link between diet and coronary heart disease, or CHD. They concluded that “simply lowering the percentage of energy from total fat in the diet is unlikely to improve lipid profile or reduce CHD incidence.” The review points to three dietary strategies effective in preventing CHD: using non-hydrogenated oils as the predominant source of dietary fat; whole grains as the main source of carbohydrates, with an abundance of fruits and vegetables; and adequate omega-3 fatty acids from sources such as fish, fish oil supplements, flax and chia seeds or walnuts.

The Ketogenic Diet Approach

Dating back to the early 1920s, the ketogenic diet began as a nonpharmacological treatment for intractable epilepsy in children and is still used this way today. Recent research has shown that regardless of age, seizure type or etiology, this diet appears to provide one-third of patients with more than 90-percent reduction in seizure frequency. Once used as the last treatment option after three or more anticonvulsant medications were unsuccessful, the ketogenic diet’s clinical management was revised by an international study group consisting of 26 physicians and registered dietitians who convened in 2006 to compile the Consensus Statement for the Ketogenic Diet. The expert panel recommended that the ketogenic diet be an earlier treatment option, especially in difficult-to-treat epilepsy patients.

The ketogenic diet has a wide following for waistline watchers, but medical supervision is important due to its extreme nature. Starting with fewer than 20 grams of carbohydrate per day, the diet’s goal is to eliminate the carbohydrate reservoir stored in muscles for energy and to force the body to use fat stores instead, through a process called ketosis. Putting the body in a state of ketosis has shown to decrease hunger and satisfy appetite longer, but doing so may increase risk factors for heart disease by elevating blood lipids, such as low-density lipoprotein cholesterol, or LDL-C. According to a 2005 trial published in Diabetologia, LDL-C increased by more than 10 percent in 25 percent of the participants who were on a ketogenic diet. Although in the short term the ketogenic diet may aid in weight loss, long-term adherence to this high-fat, low-carbohydrate plan may be detrimental to heart health and emotional well-being, as imposing severe food restrictions may create a stronger desire for so-called “forbidden” foods.

The ketogenic diet consists mainly of fat from meat, poultry, fresh fish and shellfish, whole eggs, most types of cheese, moderate amounts of nuts, any oils, butter, cream and mayonnaise. To keep carbohydrate intake low, vegetables such as leafy greens, broccoli, cauliflower and celery are the only source allowed — starchy vegetables, such as peas, corn or potatoes, as well as high-sugar peppers, onions and tomatoes, are off limits. To replace sugar, non-nutritive sweeteners such as stevia and liquid sweeteners with zero calories or carbohydrates are allowed.

Different forms of the ketogenic diet exist, but the “classic” form is the most used and widely researched. In this version, fat is derived from foods rich in long-chain triglycerides, such as butter, whipping cream, mayonnaise and olive or canola oils. Protein intake is determined by minimum requirements for growth, and carbohydrates are restricted. The classic ketogenic diet ratio is 4 grams of fat to 1 gram of protein and carbohydrates, or 90 percent of calories from fat and 10 percent from protein and carbohydrates combined.

Since this diet falls well above the AMDR for fat and restricts foods rich in certain nutrients, risks associated with it include elevated lipids in the blood, particularly LDL-C, as well as kidney stones, bone fractures due to low calcium and vitamin D intake, and constipation due to lack of fiber-rich whole grains, fruits and some vegetables. Since the macronutrient distribution of this diet is unbalanced, vitamin and mineral supplementation is often necessary, especially calcium, vitamin D, iron and folic acid.

The Bottom Line

Significantly altering the amount of fat in the diet has many implications. The AMDR for fat exists to ensure a safe range of nutrient intakes and decrease the risk of chronic diseases. Balance in macronutrient distribution works best for maintaining a healthy body weight and overall health. As with all nutrition recommendations, the amount of fat an individual should consume is based on unique needs in relation to the person’s age, gender and activity level, as well as special health needs. It is the role of the registered dietitian nutritionist to guide clients toward a safe, health-optimizing lifestyle through personalized nutrition.

Being well-versed in these fat-extreme diets is important, as working with candidates for either eating plan requires understanding of how the diet works and its potential benefits and risks.

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Vicki Shanta Retelny
Vicki Shanta Retelny, RDN, is a lifestyle nutrition expert, author, speaker, recipe and content creator based in Chicago. She blogs at Follow her on Instagram, Facebook and Twitter.