A Cautionary Tale: When Fat Consumption Goes Too Far

In January 2025, a striking case published in JAMA Cardiology [1] sent shockwaves through the nutrition community.1 A man in his 40s, following an extreme version of the carnivore diet, developed an alarming condition after just eight months of consuming massive quantities of animal fats—including up to 2.7-4.1 kg (6-9 pounds) of cheese, multiple sticks of butter, and fat-laden hamburgers daily.

Despite initially experiencing what seemed like positive effects—weight loss, increased energy, and improved mental clarity—his body told a different story. Yellow nodules appeared on his palms, soles, and elbows, a condition known as xanthelasma [2, image]. Most concerning was his cholesterol level, which skyrocketed from an already elevated baseline of 5.4-7.8 mmol/L (210-300 mg/dL) to over 25.9 mmol/L (1,000 mg/dL)—a level that set off immediate medical alarm bells.

This case serves as a powerful reminder that even when a diet makes us feel good initially, the long-term consequences can be severe. Let's explore why this happens and how we can make better choices about dietary fat.

Understanding Dietary Fats

Fats come in various forms, each with distinct characteristics and nutritional profiles:

Saturated fats (associated with poor health)

- Red meat (beef, lamb, pork)

- Full-fat dairy products (butter, cheese, cream)

- Lard

- Coconut and palm oil

Unsaturated fats (associated with good health)

- Fatty fish

- Duck and Chicken dark meat (especially the skin)

- Olive, sunflower and soybean oil

- Avocados

- Nuts

- Seeds

- Egg yolks

Cholesterol: Found exclusively in animal products, with highest levels in:

- Organ meats

- Shellfish

- Egg yolks

Natural trans fats (also known as ruminant trans fats): Present in small amounts in:

- Beef and lamb (approximately 3-5% of total fat content)

- Dairy products like butter and cheese (2-5% of total fat content)

- Note: These natural trans fats, such as conjugated linoleic acid (CLA), are different from artificial trans fats found in processed foods

The Carnivore Diet Phenomenon

The carnivore diet, as illustrated by the JAMA case study, represents an extreme approach to nutrition that eliminates all plant-based foods in favor of animal products exclusively. While proponents claim benefits like:

- Mental clarity

- Weight loss

- Increased energy

- Reduced inflammation

The diet gained momentum through social media influencers and certain medical professionals. However, as the recent case study demonstrates, the risks can far outweigh any perceived benefits, especially when taken to extremes.

Beyond Carnivore: High-Fat Diets in Context

The landscape of high-fat diets extends well beyond the carnivore approach. Several well-known dietary patterns emphasise fat consumption:

Ketogenic Diet

Originally developed for epilepsy treatment, the ketogenic diet typically consists of 70-80% calories from fat. Unlike the carnivore diet, it includes plant-based fats and limited carbohydrates.

Atkins Diet

A pioneering low-carb approach that begins with severe carbohydrate restriction but gradually reintroduces them. It emphasises protein and fat while controlling carb intake.

Fat Adaptation in Sports

The concept of training the body to utilise fat for fuel gained traction in endurance sports. However, recent research has revealed limitations [3]:

- Reduced high-intensity performance capacity

- Compromised carbohydrate metabolism

- Limited benefits for most athletes except in ultra-endurance events

The Essential Role of Dietary Fat

Fat serves numerous crucial functions in human health:

1. Energy Storage and Production

- Provides 9 calories per gram, making it an efficient energy source

- Essential for maintaining body temperature

- Supports hormone production

2. Nutrient Absorption

- Enables absorption of fat-soluble vitamins (A, D, E, K)

- Enhances bioavailability of certain nutrients

3. Cell Structure and Function

- Forms cell membranes

- Supports brain health and nervous system function

- Produces essential hormones

Optimising Fat Intake for Health and Performance

Finding the right balance with dietary fat involves several key principles:

For General Health:

1. Diversify Fat Sources

- Include both plant and animal sources

- Focus on quality

- Consider fatty fish for omega-3s

2. Monitor Portions

- Aim for 20-35% of total daily calories from fat

- Pay attention to serving sizes of high-fat foods

For Exercise Performance

1. Training Adaptation

- Adjust fat intake based on training phase and goals

- Higher fat intake during base training may enhance fat oxidation

- Increase carbohydrates during high-intensity training periods.

2. Timing Considerations

- Moderate fat intake before exercise to prevent digestive issues

- Include healthy fats in post-exercise meals for recovery

Practical Implementation

- Choose whole food sources over processed options

- Include a variety of fat sources throughout the day

- Consider individual tolerance and digestive comfort

- Monitor performance and energy levels

- Adjust intake based on personal goals and response

Remember that optimal fat intake varies among individuals based on factors like:

- Activity level

- Metabolic health

- Personal goals

- Genetic factors

- Overall dietary pattern

The key is finding a sustainable approach that supports both health and performance goals while avoiding extremes that could compromise long-term wellbeing.

Research

1. Marmagkiolis K, Caballero J, Iliescu C. Hypercholesterolemia and Xanthelasma Associated With a Carnivore Diet. JAMA Cardiol. Published online January 22, 2025.

2. Images sourced from JAMA article

3. Burke LM, Whitfield J, Heikura IA, Ross MLR, Tee N, Forbes SF, Hall R, McKay AKA, Wallett AM, Sharma AP. Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability. J Physiol. 2021 Feb;599(3):771-790. doi: 10.1113/JP280221. Epub 2020 Aug 19. PMID: 32697366; PMCID: PMC7891450.