Carbs vs. Fat
Posted by Mira on April 29, 2025
(This is a summary of my understanding of carbs vs fat after looking into the human physiology and consulting with many carnivore dieters. It may not be perfect, but I hope it can help you understand the science behind why the carnivore diet works.)
In this article, I will primarily address why the carnivore diet can be a viable alternative energy source, or even a better one than the Standard American Diet (SAD), which is high in carbohydrates. I will explain why this approach works best for weight loss and metabolic health. The science behind it differs significantly from the outdated (and incorrect) metabolic understanding of Calories In, Calories Out (CICO).
Contents
Energy Sources
The human body has 2 primary sources of energy: carbohydrates (carbs), fat (including both dietary fat and stored body fat). Carbohydrates include foods such as noodles, bread, and sugar. Fats are found in foods such as butter and animal fat. The body primarily burns either carbs or fat and consistently prioritizes burning carbs first, followed by fat.
How does the body decide to burn carbs? Through insulin. Every time we eat, insulin is released. Eating carbs stimulates the most insulin release, protein stimulates a moderate amount, and fat stimulates the least. When insulin is high, the body prioritizes burning carbohydrates.
Insulin is a hormone produced by the pancreas that acts like a key, allowing glucose (sugar) from the blood to enter cells, particularly in muscle, fat, and liver tissues.
Glycolysis
When insulin is high, your body is in glycolysis mode, meaning it uses glucose for energy. Glucose (derived from carbohydrates) is moved into cells to lower blood sugar levels. Glucose is directly used by the cells as fuel. However, any excess glucose that the body does not immediately burn is converted into body fat in two main ways:
- In the liver and muscles, it is stored as glycogen, a short-term energy reserve.
- Once glycogen stores are full, the liver converts the remaining glucose into fatty acids through a process called de novo lipogenesis. These fatty acids are then stored as triglycerides in fat cells (adipose tissue).
Additionally, high insulin levels suppress the burning of stored body fat by inhibiting the activity of hormone-sensitive lipase — an enzyme responsible for breaking down stored fat (triglycerides) into free fatty acids for energy.
Ketosis
When insulin is low, you enter a state called ketosis. In ketosis, the body relies more on fat for fuel, as glucose availability is low. The body increases the metabolic rate, breaks down fat into fatty acids and produces ketones, which serve as an alternative energy source. Some ketones are excreted through urine, breath, and sweat. Once the energy from consumed dietary fat is used, the body turns to its stored fat reserves for fuel. This is one reason why people can lose weight on a carnivore diet, which is typically low in carbohydrates and keeps insulin levels low.
Eating fat can promote satiety, which helps reduce cravings and hunger. When you consume fat, your body releases hormones like leptin and cholecystokinin (CCK) that signal to your brain that you’re full. Eating fatty meat until you’re comfortably full can help you avoid overeating.
In short, carbohydrates cause insulin to spike, which leads to excess glucose being stored as body fat. On the other hand, consuming fat does not significantly spike insulin, allowing the body to burn the consumed fat first and then tap into stored body fat for energy.
All of these concepts will help guide you in understanding why you eat, what you eat, and how you eat.
Carbs vs. Fat: Which is the Better Energy Source?
Let’s break it down in simple terms.
Carbohydrates
Carbohydrates are like quick-burning fuel. When you eat carbs, your body gets fast energy — perfect for short bursts of activity, like sprinting or high-intensity workouts.
But carbs come with a catch:
- Carbs spike insulin levels, causing your body to prioritize burning carbs and store excess as body fat.
- Energy crashes often follow once the carbs are used up, leaving you hungry again.
- Eating too many carbs, especially refined ones, can lead to:
- Insulin resistance
- Type 2 diabetes
- Weight gain
- Chronic inflammation
- Fatty liver disease
- Higher risk of heart disease
- Over time, a high-carb diet can push your metabolism out of balance.
Fat
Fat is like slow-burning fuel. It provides steady, reliable energy without the ups and downs of carbs.
Benefits of using fat for energy:
- Minimal impact on insulin, so your body keeps burning fat.
- Increased satiety, helping you feel full longer and reduce cravings.
- Taps into stored body fat, supporting weight loss and metabolic health.
Overall, for athletes who need quick bursts of energy, some carb intake can be beneficial. However, for most people, especially in everyday life, carbs can easily become addictive — and the risks often outweigh the benefits. Excessive carb consumption is linked to weight gain, insulin resistance, and energy crashes.
On the other hand, fats provide a much better overall fuel source. With fat as your primary energy source, you can enjoy steady energy, better appetite control, and improved metabolic health.
