An extremely low-fat (ELF) dietary pattern is typically defined as one where fat provides 10% to 15% or less of a person’s total daily calories. This approach gained popularity in the 1970s and 1980s, driven by the belief that dietary fat caused obesity and heart disease. While reducing unhealthy saturated and trans fats is beneficial, severely restricting total fat intake can introduce several unintended physiological and practical complications.
Impaired Absorption of Fat-Soluble Vitamins
Fats in the diet play a fundamental role in the body’s ability to absorb four specific micronutrients: Vitamins A, D, E, and K. These are called fat-soluble vitamins because they cannot be absorbed efficiently without dietary fat acting as a necessary carrier. In the small intestine, dietary fats allow these vitamins to dissolve and be transported across the intestinal lining into the bloodstream. Without sufficient dietary fat, this transport mechanism is significantly hindered, leading to malabsorption and chronic deficiency.
Chronic deficiency in these vitamins impacts several bodily systems. Vitamin A supports vision and immune function. Vitamin D is crucial for regulating calcium and phosphorus metabolism, thereby supporting bone health.
Vitamin E acts as an important antioxidant and supports nerve and muscle function. Vitamin K is vital for the liver’s synthesis of blood-clotting factors. An ELF diet systematically interferes with the body’s ability to utilize these protective nutrients.
Deficiency of Essential Fatty Acids
The body requires specific types of fat, known as Essential Fatty Acids (EFAs), that it cannot produce on its own and must obtain from food. The two primary EFAs are linoleic acid (omega-6) and alpha-linolenic acid (omega-3). These fats are fundamental structural components of every cell, incorporated into the cell membrane to influence its fluidity and permeability, which is necessary for proper cellular communication.
The brain and nervous system rely heavily on these structural fats, as nerve cells are insulated by a fat-rich lining. Compromised intake can therefore affect mood and cognitive function. EFAs are also precursors for eicosanoids, hormone-like substances that regulate inflammation, blood clotting, and other metabolic functions. A deficiency impairs the body’s ability to manage its inflammatory response. Visible signs of prolonged EFA deficiency often manifest in dry, flaky skin and brittle hair.
Disruption to Hormonal Regulation
Dietary fat is intrinsically linked to the endocrine system because fat and cholesterol serve as necessary precursors for all steroid hormones. Cholesterol is the parent molecule from which the body synthesizes hormones like estrogen, testosterone, and cortisol. Severely restricting fat intake can deprive the body of the raw materials needed for adequate hormone production and regulation.
An ELF diet has been shown to reduce levels of sex hormones, leading to reproductive and metabolic issues. In men, this diet is associated with decreased testosterone levels. For women, it can significantly lower circulating estrogen, potentially causing menstrual irregularities or amenorrhea (loss of a menstrual period). The overall impact extends to metabolic function, often resulting in sluggish metabolism and reduced energy levels. Furthermore, the production of leptin, which regulates appetite and reproductive hormones, can be suppressed, compounding the hormonal imbalance.
Challenges with Satiety and Adherence
Beyond the physiological impacts, extremely low-fat diets present significant practical and psychological hurdles that make them difficult to sustain long-term. Fat is a macronutrient that plays a major role in promoting satiety, or the feeling of fullness, compared to an equal volume of carbohydrates or protein. Fat digestion stimulates the release of gut hormones like cholecystokinin (CCK) and peptide YY (PYY), which signal to the brain that the stomach is full, and delays gastric emptying.
When fat is severely restricted, this powerful satiety signaling is diminished, often leading to increased feelings of hunger throughout the day. To compensate for the low caloric density of fat-restricted foods, individuals frequently increase their intake of carbohydrates, often choosing refined carbohydrates and added sugars. This shift can cause rapid insulin spikes and may lead to non-alcoholic fatty liver disease (NAFLD) and increased body fat storage.
The palatability of food also suffers greatly when fat is removed, making the diet less pleasurable and harder to adhere to, which is a common cause of diet failure. The combination of persistent hunger, the need to overeat carbohydrates to feel full, and the resulting low mood or “brain fog” due to poor lipid intake creates a challenging cycle. This makes the ELF diet a pattern that is often abandoned, despite initial intentions for better health.