What Will Happen if You Eat Less Fat? Surprising Health Effects

October 6, 2025 •

4 min read

According to a 2016 study, a very low-fat intake of less than 15% of daily calories was associated with a higher incidence of metabolic syndrome. This surprising finding reveals that cutting out too much fat can have significant negative health consequences, directly impacting key bodily functions, and showing what will happen if you eat less fat.

Quick Summary

This article explores the potentially severe health repercussions of reducing dietary fat too much, including hormonal dysfunction, cognitive decline, and nutrient deficiencies. It outlines the differences between healthy and unhealthy fats, offers a comparison of dietary patterns, and provides guidance for maintaining optimal health.

Key Points

Hormonal Imbalance: Severe restriction of fat can disrupt hormone production, leading to issues like irregular periods in women and lower testosterone in men.
Cognitive Decline: The brain, composed of significant fat, can suffer from insufficient fat intake, causing symptoms like brain fog, difficulty concentrating, and mood swings.
Vitamin Deficiencies: A low-fat diet hinders the absorption of fat-soluble vitamins (A, D, E, and K), increasing the risk of associated health problems.
Skin and Hair Problems: Without enough fat, skin can become dry and flaky, and hair may become brittle, as fat is crucial for maintaining skin moisture and hair health.
Increased Hunger and Cravings: Fat provides satiety, so reducing it too drastically can lead to constant hunger and increased cravings for sugary or refined carbohydrates.
Misleading 'Low-Fat' Products: Many processed low-fat foods compensate for lost flavor by adding sugar and refined carbs, which can be detrimental to health and weight management.
Choose Quality Over Quantity: The focus should be on replacing unhealthy saturated and trans fats with healthy monounsaturated and polyunsaturated fats, rather than simply reducing overall fat intake.

The Importance of Dietary Fat for Your Body

Despite decades of misguided demonization, dietary fat is a critical macronutrient essential for survival, not the enemy of health. Your body relies on fats for numerous biological processes, from providing sustained energy to absorbing fat-soluble vitamins (A, D, E, K), which would be impossible without it. Healthy fats are fundamental building blocks for cell membranes throughout your body and act as precursors to vital hormones like estrogen and testosterone. Understanding this foundational role is the first step in appreciating why cutting out too much fat is problematic.

Impact on Hormones and Reproduction

One of the most profound effects of eating too little fat is a hormonal imbalance. For women, an extremely low body fat percentage and insufficient fat intake can lead to hypothalamic amenorrhea, causing the menstrual cycle to stop completely. The body conserves energy for essential functions, deeming reproduction non-essential. Men can also experience negative effects, including decreased testosterone levels, which can lead to reduced libido and chronic fatigue. The cholesterol from dietary fat is a necessary building block for these sex hormones, and without it, production stalls.

Effects on Brain and Mental Health

Your brain is roughly 60% fat and requires a consistent supply of fatty acids to function properly. A severe reduction in fat intake can lead to a number of cognitive and mental health issues. Signs of this can include 'brain fog,' difficulty concentrating, and mood swings. Essential omega-3 fatty acids are critical for maintaining the structural integrity of brain cells and supporting overall cognitive function. Low intake of omega-3s, which are often found in healthy fat sources, has been linked to an increased risk of depression and other psychiatric disorders.

Poor Nutrient Absorption and Appearance

As mentioned, fats are crucial for the absorption of the fat-soluble vitamins A, D, E, and K. Without enough fat, your body cannot absorb these nutrients effectively, potentially leading to a deficiency even if you're eating a diet rich in them. This can manifest in several ways:

Dry, flaky skin: Fat forms a protective barrier for skin cells, maintaining moisture and preventing dryness.
Brittle hair: Essential fatty acids contribute to healthy hair growth and shine.
Compromised immunity: Some fatty acids play a role in regulating inflammation and immune cell function, making you more susceptible to illness when deficient.

The Double-Edged Sword of Low-Fat Products

Ironically, attempting to eat less fat can sometimes backfire. When food manufacturers remove fat from products, they often replace it with added sugar or refined carbohydrates to maintain flavor. This can lead to rapid blood sugar fluctuations, increased cravings, and ultimately, weight gain. Furthermore, these highly processed, low-fat versions can be nutrient-poor compared to their whole-food counterparts.

Comparison of Dietary Fat Intakes


Feature	Low-Fat Diet (Under 20-30% calories)	Moderate-Fat Diet (30-40% calories)
Energy	Initially high in carbohydrates, may lead to energy crashes.	Balanced energy from fats, proteins, and carbs, leading to sustained energy.
Satiety	Fat is satiating; low-fat meals often leave you hungry sooner.	Increased feeling of fullness, which can help manage calorie intake naturally.
Nutrient Absorption	Reduced absorption of fat-soluble vitamins (A, D, E, K).	Optimal absorption of essential fat-soluble vitamins.
Hormonal Health	Potential for hormonal imbalance, affecting mood and reproduction.	Better support for hormone production and balance.
Brain Function	Can lead to brain fog and impaired concentration.	Provides essential fatty acids for optimal brain function.

How to Eat Less Bad Fat Effectively

Instead of eating less fat overall, a better approach is to focus on the quality of fat you consume. The goal is to limit unhealthy trans fats and saturated fats while increasing beneficial unsaturated fats. Here’s how to do it effectively:

Swap unhealthy for healthy fats: Replace sources of saturated fat (like fatty meats and full-fat dairy) with sources of unsaturated fats (like olive oil, avocados, nuts, and seeds).
Read labels carefully: Watch out for products labeled 'low-fat' that may have high sugar content. Choose whole foods instead.
Portion control: All fats are calorie-dense. While healthy, they should still be consumed in moderation as part of a balanced diet.

Conclusion: The Moderation Mindset

The old mentality that 'less fat is better' has been widely debunked. Instead of asking what will happen if you eat less fat, a better question is: what happens if you eat the right kinds of fat in the right amounts? A diet too low in fat, particularly healthy unsaturated fats, can lead to serious health problems, including hormonal and neurological issues. The key lies in moderation and quality, focusing on a balance of macronutrients from whole food sources to fuel your body effectively. Making intelligent choices about fat intake is crucial for long-term physical and mental well-being.

Learn more about making smart fat choices from trusted nutrition resources.

Frequently Asked Questions

While fat is calorie-dense, simply eating less fat doesn't guarantee weight loss. Many low-fat products are high in sugar and refined carbs, which can lead to blood sugar spikes, increased hunger, and weight gain. Focusing on a balanced diet with healthy fats is more effective for long-term weight management.

Research suggests that replacing saturated fats with unsaturated fats can improve heart health by lowering 'bad' LDL cholesterol. However, eating too little fat overall can ironically lead to less favorable heart health markers, including changes to LDL particle size.

Common symptoms of insufficient fat intake include dry skin and hair, joint pain, constant hunger, increased fatigue, getting sick more often, and brain fog. These are signs your body is missing essential fatty acids and fat-soluble vitamins.

Healthy fats are primarily monounsaturated and polyunsaturated fats. They are found in foods like avocados, nuts, seeds, fatty fish (salmon, tuna), and vegetable oils (olive, canola). These fats support brain function, heart health, and reduce inflammation.

No, fats are essential for hormone production. Healthy fats, particularly from sources like fatty fish and nuts, provide the building blocks needed for hormones like estrogen and testosterone. Severely restricting fat can cause hormonal imbalances.

Studies have linked low intake of essential omega-3 fatty acids, often a result of low-fat dieting, with an increased risk of depression and other mood disorders. A lack of fat can impair brain communication and mood regulation.

For most adults, fat should account for about 20-35% of total daily calories, according to the Dietary Guidelines for Americans. This range ensures adequate intake of essential fatty acids and fat-soluble vitamins, while a balanced approach is more important than strict numbers.