What Happens If You Cut Out Fat? The Surprising Risks of Fat Deficiency

December 13, 2025 •

4 min read

Despite popular 90s diet trends, eliminating all dietary fat is not a healthy or sustainable approach and can lead to significant health complications. Understanding what happens if you cut out fat is crucial, as this macronutrient plays a vital role in everything from hormonal balance to vitamin absorption.

Quick Summary

Removing fat from your diet can cause a range of issues, including fat-soluble vitamin deficiencies, hormonal imbalances, poor skin health, and impaired cognitive function, often leading to increased hunger and overall fatigue. Achieving a balanced diet is key.

Key Points

Vitamin Absorption: Cutting out fat impairs the body's ability to absorb essential fat-soluble vitamins A, D, E, and K, which can lead to deficiencies.
Hormonal Imbalances: A very low-fat diet can disrupt the production of crucial steroid hormones like estrogen and testosterone.
Skin and Hair Health: Fat is necessary for healthy, hydrated skin and strong hair; deficiency can cause dryness, rashes, and hair loss.
Cognitive Function: Essential fatty acids are vital for brain health, and cutting fat can lead to issues like brain fog and mood swings.
Appetite Regulation: Fat promotes satiety, and without it, you may experience increased hunger and cravings, which can undermine weight management efforts.
Weakened Immunity: Inadequate fat intake can compromise the immune system, making you more susceptible to frequent illnesses.

The Vital Roles of Dietary Fat

For years, dietary fat was demonized as the primary cause of weight gain and heart disease, leading many to attempt to cut it out entirely. However, fat is a crucial macronutrient that performs several essential functions in the body. It is not a matter of whether you should eat fat, but rather what type of fat and in what quantity.

Energy and Satiety

Fat is a concentrated source of energy, providing 9 calories per gram—more than twice that of carbohydrates or protein. This high energy density helps the body perform daily activities and fuels endurance exercise. Additionally, fat slows down digestion, which helps you feel full and satisfied for longer after a meal, aiding in appetite control.

Essential Fatty Acids and Absorption

Fats are the only way the body can absorb the fat-soluble vitamins A, D, E, and K. Without enough fat in the diet, you can become deficient in these crucial vitamins, leading to a cascade of health issues. Fats also supply essential fatty acids, like omega-3 and omega-6, which the body cannot produce on its own and are critical for cell structure, brain health, and managing inflammation.

Hormonal Function and Brain Health

Fats are the building blocks for hormones, including vital sex hormones like estrogen and testosterone. Restricting fat intake can disrupt this production, leading to hormonal imbalances that manifest as irregular menstrual cycles in women and decreased libido in men. Furthermore, the brain is composed of about 60% fat, making healthy fats indispensable for cognitive function, mood regulation, and memory.

The Negative Consequences of a Very Low-Fat Diet

When you cut out too much fat, your body quickly begins to show signs of deficiency. These can range from minor discomforts to serious long-term health problems.

Common Symptoms of Inadequate Fat Intake:

Dry, Flaky Skin and Hair Loss: Fat is essential for maintaining the moisture barrier of skin cells and promoting hair growth.
Increased Hunger and Cravings: Without fat to promote satiety, you may experience frequent hunger and intense cravings for carbohydrates and sugar.
Cognitive Issues (Brain Fog): Reduced intake of essential fatty acids can impair brain function, leading to difficulty concentrating and mental fogginess.
Weakened Immune System: Essential fatty acids and fat-soluble vitamins are crucial for immune cell function. Insufficient fat can leave you more susceptible to illness.
Hormonal Imbalances: As mentioned, sex hormone production can be disrupted, leading to issues like irregular periods and low libido.
Fatigue and Low Energy: Since fat is a dense energy source, a very low-fat diet can significantly reduce overall calorie intake and leave you feeling constantly tired.

Comparison: Balanced Fat Intake vs. Very Low-Fat Diet


Aspect	Balanced Fat Diet (20-35% of calories from fat)	Very Low-Fat Diet (<15% of calories)
Energy Levels	Sustained and stable energy.	Frequent energy crashes and fatigue.
Hormonal Balance	Supports optimal hormone production.	Risk of disrupting steroid hormone synthesis.
Vitamin Absorption	Maximizes absorption of fat-soluble vitamins (A, D, E, K).	Impairs absorption, risking deficiencies.
Appetite Regulation	Promotes satiety and helps control cravings.	Can lead to increased hunger and cravings.
Cardiovascular Health	Healthy fats (unsaturated) improve heart health markers.	Can negatively impact heart health by altering cholesterol profile.
Skin & Hair	Contributes to healthy, moisturized skin and strong hair.	Causes dry, flaky skin and potential hair loss.
Brain Function	Provides essential fatty acids crucial for cognitive health.	Linked to potential cognitive issues and mood swings.

How to Achieve a Healthy Fat Balance

Instead of aiming to cut out fat, the focus should be on replacing harmful saturated and trans fats with beneficial unsaturated fats. A balanced approach ensures you receive all the health benefits fat offers without the risks associated with deficiency.

Sources of Healthy Fats:

Monounsaturated Fats: Found in avocados, olive oil, nuts (almonds, cashews), and seeds.
Polyunsaturated Fats (Omega-3 and Omega-6): Found in fatty fish (salmon, mackerel), flaxseeds, walnuts, and sunflower oil.
Other Sources: Whole eggs, dark chocolate, and tofu also provide healthy fats.

For more information on dietary guidelines, consult reputable health organizations like the World Health Organization.

Conclusion: The Importance of Fat for Overall Health

Cutting out fat entirely is not only ineffective for long-term health but can also be genuinely harmful. From compromised hormonal function and nutrient absorption to skin issues and cognitive decline, the body’s reliance on fat is clear. A balanced, sustainable approach that prioritizes healthy fats and limits unhealthy ones is the key to supporting overall wellness and avoiding the serious health consequences of deficiency. It is time to move past the era of "low-fat" and embrace the vital role of this essential macronutrient.

Frequently Asked Questions

Some of the first signs of inadequate fat intake include dry, flaky skin, increased feelings of hunger shortly after meals, frequent fatigue, and difficulty concentrating.

Yes, a very low-fat diet can significantly affect your hormone production, particularly sex hormones like estrogen and testosterone, which can lead to irregular menstrual cycles and decreased libido.

If you cut out fat, your skin may lose its moisture barrier, leading to dryness, scaliness, and potentially skin inflammation like dermatitis.

Yes, restricting fat intake can weaken your immune system. Essential fatty acids support immune cell function, and their deficiency can leave you more vulnerable to illness.

Fats are required to absorb fat-soluble vitamins (A, D, E, and K). Without sufficient dietary fat, your body cannot absorb these vitamins effectively, leading to potential deficiencies.

Excellent sources of healthy fats include avocados, olive oil, nuts, seeds (flaxseeds, chia seeds), and fatty fish like salmon.

No, this is a myth. While some fats, like trans fats and excessive saturated fats, are unhealthy, unsaturated fats are vital for good health. A balanced intake of healthy fats is essential for your body to function properly.

Fats digest more slowly than carbohydrates and protein, which helps promote a feeling of fullness. When you cut out fat, food moves through your system faster, and you may feel hungrier more quickly.