What Happens to Your Body If You Eat Less Fat?

December 7, 2025 •

4 min read

According to a study published in The BMJ, reducing total fat intake was associated with small but significant and sustained reductions in body weight. However, the reality of what happens to your body if you eat less fat is more complex, impacting everything from hormone production to nutrient absorption.

Quick Summary

A diet low in fat can lead to sustained weight loss but also introduces risks like nutrient deficiencies and metabolic issues. The effects depend heavily on whether healthy fats are replaced with nutrient-poor alternatives or wholesome foods.

Key Points

Weight Loss Potential: Reducing fat intake can help with weight management by decreasing overall calorie consumption.
Risk of Vitamin Deficiencies: A diet severely lacking in fat can impair the absorption of fat-soluble vitamins A, D, E, and K.
Hormonal Imbalance: Fats are necessary for hormone production, and low-fat diets can potentially disrupt hormonal balance, especially in men.
Mental Health Concerns: The brain requires healthy fats for proper function; extreme restriction can be linked to mood and mental health issues.
Metabolic Downsides: Replacing fat with refined carbohydrates in processed foods can lead to unfavorable metabolic changes, like increased triglycerides.
Skin and Hair Health: Lack of essential fatty acids from a very low-fat diet can result in poor wound healing, skin problems, and hair loss.

The Dual Nature of Dietary Fat

For decades, fat was demonized as the primary cause of obesity and heart disease, leading to a surge in low-fat food products. We now understand that not all fats are created equal and that healthy fats are essential for a wide range of bodily functions. Severely restricting fat intake can trigger a complex cascade of physiological changes. This article explores the nuanced effects of reducing dietary fat, from the intended weight loss benefits to the hidden health risks.

Potential Benefits of a Low-Fat Diet

When done correctly, reducing unhealthy fat consumption can offer several health advantages. The key is to replace unhealthy fats, like saturated and trans fats found in processed foods, with nutrient-dense, fiber-rich whole foods.

Weight Management: Since fat contains more than double the calories per gram of carbohydrates and protein, simply reducing fat intake can create a calorie deficit, leading to weight loss. Studies have shown a correlation between lower fat intake and reduced body mass index (BMI).
Improved Cardiovascular Health: Decreasing your intake of saturated and trans fats can lower total blood cholesterol and LDL (“bad”) cholesterol levels, which are significant risk factors for heart disease. Replacing these with unsaturated fats can further improve your cholesterol profile.
Increased Nutrient Intake: By replacing high-fat processed snacks with fruits, vegetables, and whole grains, you naturally increase your fiber, vitamin, and mineral intake. This shift supports better gut health, appetite control, and overall nutrition.

Significant Risks of Cutting Too Much Fat

While the benefits are clear, drastically cutting all fat can lead to unintended health problems. Your body relies on fats for crucial functions, and deprivation can disrupt these systems.

Vitamin Deficiencies: Vitamins A, D, E, and K are fat-soluble, meaning they require dietary fat for absorption. A severely low-fat diet can hinder this process, potentially leading to deficiencies that affect vision, bone density, immune function, and blood clotting.
Hormonal Imbalances: Fats are fundamental building blocks for many hormones, including reproductive hormones like testosterone. For men, a very low-fat diet has been linked to significantly lower testosterone levels. Such hormonal shifts can impact sexual health, mood, and bone mass.
Mental Health Issues: Your brain is approximately 60% fat, and it relies on healthy fats for optimal function. Severely low cholesterol levels, often a side effect of extremely low-fat diets, have been linked to increased impulsivity and mood disorders.
Unfavorable Metabolic Changes: When fats are removed from processed foods, they are often replaced with sugar, salt, and refined carbs to maintain flavor. A diet high in these unhealthy carbs can lead to increased triglycerides and reduced HDL (“good”) cholesterol, potentially increasing the risk of metabolic syndrome.
Hair and Skin Problems: Healthy fats are vital for cell growth and wound healing. Extremely low-fat diets can lead to poor skin quality, and deficiencies in certain fatty acids can contribute to hair loss.

Comparison: Healthy Fat vs. Unhealthy Fat Intake


Feature	Eating Enough Healthy Fats	Eating Excessive Unhealthy Fats	Severely Restricting All Fat
Weight Management	Supports weight loss by promoting satiety.	Contributes to weight gain and obesity.	Can lead to weight loss, but with potential deficiencies.
Cholesterol Levels	Improves HDL and reduces LDL.	Increases LDL ("bad") cholesterol.	Can cause unfavorable metabolic changes.
Nutrient Absorption	Essential for absorbing fat-soluble vitamins (A, D, E, K).	Does not guarantee proper vitamin absorption if unhealthy.	Significantly impairs absorption of fat-soluble vitamins.
Hormone Production	Crucial for hormone synthesis.	Disrupts hormonal balance.	Disrupts hormone synthesis, especially reproductive hormones.
Mental Health	Supports brain function and mood regulation.	Can be linked to poor mental health outcomes.	Can negatively affect mood and mental health.

The Importance of Balance

Eliminating fat entirely is neither necessary nor healthy. The key is to focus on a balanced approach that prioritizes nutrient-dense foods and healthy fats while limiting unhealthy ones. Incorporating sources of monounsaturated and polyunsaturated fats—such as avocados, nuts, seeds, and fatty fish—is vital for supporting your body's essential functions. A registered dietitian can help you find the right balance for your individual needs.

Conclusion: Finding the Right Path for You

What happens to your body if you eat less fat is not a simple story of good or bad, but a complex interplay of benefits and risks. While reducing unhealthy fats can aid in weight loss and cardiovascular health, the extreme restriction of all fats can cause serious deficiencies, hormonal problems, and mental health issues. A well-balanced diet that includes healthy fats is essential for long-term well-being. Ultimately, focusing on high-quality, whole foods and moderating your intake of processed products will lead to the best outcomes for your body and mind.

Visit the Banner Health blog for more information on low-fat diets.

Frequently Asked Questions

Not necessarily. While fat is calorie-dense, replacing it with high amounts of refined carbohydrates and sugar can negate weight loss efforts and lead to other metabolic issues.

A deficiency in fat-soluble vitamins (A, D, E, K) can impact your body in many ways, including vision problems, weakened immunity, poor bone health, and impaired blood clotting.

Yes, it can. Since the brain is largely composed of fat and relies on it for nerve function and mood regulation, severely restricting fat has been linked to mood disorders and impulsivity.

The research is divided. While low-fat diets can reduce bad cholesterol, focusing on replacing unhealthy fats with healthy ones and whole foods is more important than simply cutting fat or carbs.

Healthy fats can be found in avocados, nuts, seeds, and fatty fish like salmon and mackerel. These provide essential fatty acids for various bodily functions.

Fats are crucial for producing hormones like testosterone. Extremely low-fat diets have been shown to cause small but significant reductions in hormone levels, which can affect sexual health and other functions.

Yes. Manufacturers often replace fat with high levels of sugar, sodium, and refined starches to improve flavor. These additives can lead to unfavorable metabolic changes and undermine health goals.

Without sufficient essential fatty acids, you may experience slower wound healing, hair loss, and general skin issues. Fat is required for healthy cell growth.

No, it is not recommended to eliminate fat entirely. Healthy fats are vital for essential bodily functions. The focus should be on moderating unhealthy fats and prioritizing healthy ones.