The Science Behind Fat Storage, Insulin, and Appetite
For decades, weight gain has been explained with a simple formula: calories in versus calories out.
But in real life and in the scientific literature,this explanation doesn’t hold up.
People can eat similar calories and experience completely different outcomes. Some gain fat rapidly, while others remain stable. The difference isn’t discipline, motivation, or willpower.
It’s biology.
More specifically, it’s about food combinations, insulin, and how appetite and fat storage are hormonally regulated.
Fat Storage Is Hormonal — Not a Failure of Self-Control
Body fat is not stored randomly. It is tightly controlled by hormones, with insulin acting as the primary regulator.
- When insulin is elevated:
- Fat burning (lipolysis) is suppressed
- Fat storage is promoted
- Dietary fat is preferentially stored
- Access to existing body fat is restricted
This means fat gain is not simply about eating too many calories. It’s about eating in a hormonal environment that favours storage over fat oxidation.
Two meals with identical calories can produce very different metabolic outcomes depending on how strongly insulin is stimulated.
The Most Fat-Promoting Combination of Foods
From a physiological standpoint, the most fattening meals share a common pattern:
- Refined carbohydrates or sugars
- Dietary fat
- Low protein and low fibre
This combination:
- Causes a rapid rise in blood glucose
- Triggers a strong insulin response
- Delivers high energy at the exact moment fat burning is switched off
- Fails to activate satiety hormones effectively
This is the biochemical fingerprint of ultra-processed foods—and a key reason they are so strongly associated with obesity and metabolic disease.
Why Certain Foods Are Uniquely Fattening
Doughnuts, Pastries, Cakes, and Muffins
These foods combine refined flour, added sugar, and fat (often deep-fried or butter-based).
Metabolic effect:
- Rapid glucose absorption
- Large insulin release
- Immediate fat storage
Clinical pattern:
- Hunger returns quickly
- Energy crashes
- Strong cravings later in the day
This is driven by reactive hypoglycaemia following an exaggerated insulin response—not a lack of restraint.
Pizza
Pizza is metabolically deceptive.
While its glycaemic index appears moderate, mixed meals containing refined carbohydrates and fat lead to prolonged insulin elevation, suppressing fat burning for hours.
Clinical pattern:
- Difficulty stopping at one slice
- Post-meal fatigue
- Weight gain despite “not eating dessert”
This is a hormonal effect, not a calorie miscalculation.
Burgers and Fries
This combination represents one of the most efficient fat-storage meals.
- Fries: high-GI carbohydrates + oxidised oils
- Bun: refined starch
- Sauces: sugar + fat
Outcome:
A strong insulin response combined with abundant dietary fat results in highly efficient fat storage and worsens insulin resistance over time.
This pattern is strongly associated with visceral (abdominal) fat accumulation.
Chocolate Bars and Sweet Snacks
Chocolate bars are engineered for maximal reward and minimal satiety.
- High sugar
- High fat
- Very low protein
Because protein is the primary driver of fullness, these foods fail to shut down appetite, often leading to overeating despite high calorie intake.
Ice Cream
Ice cream poses a unique problem due to its structure:
- Semi-liquid sugar and fat
- Rapid gastric emptying
- Minimal chewing
This causes fast rises in blood sugar and insulin, while satiety hormones lag behind—making it unusually easy to overconsume without feeling full.
Sugary Cereals and Sweet Breakfasts
Breakfast sets the metabolic tone for the day.
High-glycaemic breakfasts:
- Spike insulin early
- Reduce fat oxidation
- Increase hunger later in the day
Clinically, this shows up as mid-morning hunger, afternoon energy crashes, and persistent cravings, especially when protein intake is low.
Why Fat and Carbohydrates Together Are Worse Than Either Alone
This distinction is critical:
Carbohydrates alone raise insulin but provide little fat to store
Fat alone produces a minimal insulin response
Carbohydrates + fat together raise insulin and deliver energy for storage
Ultra-processed foods exploit this interaction perfectly—which is why they are so effective at driving fat gain.
The Protein Leverage Hypothesis: Why Low-Protein Diets Drive Overeating
One of the strongest frameworks in appetite science is the Protein Leverage Hypothesis, proposed by Professors Stephen Simpson and David Raubenheimer.
The theory states that humans will continue eating until their protein requirement is met, regardless of total calorie intake.
When diets are diluted with refined carbohydrates and fats:
- Protein intake falls
- Hunger persists
- Total calorie intake rises unintentionally
Increasing protein intake has been shown to:
- Increase satiety hormones (PYY, GLP-1)
- Reduce the hunger hormone ghrelin
- Lower spontaneous calorie intake
- Improve body composition without conscious restriction
This explains why many people feel hungrier on low-fat, highly processed diets, even when calorie intake is adequate.
The Vicious Cycle of Insulin, Hunger, and Fat Storage
Repeated exposure to high-GI, low-protein meals leads to:
- Chronically elevated insulin
- Suppressed fat breakdown
- Increased hunger and cravings
The body signals hunger because it cannot access stored energy, even when body fat is abundant.
This is a biological trap, not a behavioural failure.
A Better Framework for Fat Loss
When nutrition is structured to:
- Prioritise protein
- Control carbohydrate quality and quantity
- Separate high-fat intake from insulin-raising meals
- Increase fibre from vegetables
We consistently see:
- Reduced hunger
- Improved insulin sensitivity
- Easier fat loss
- Better energy and mental clarity
Not because people are “trying harder” but because the hormonal environment finally supports fat burning.
Where Be Fit Food Fits — By Design
Be Fit Food was created from this exact scientific and clinical understanding.
Every meal is designed to:
* Be protein-first
* Cap carbohydrates to minimise insulin spikes
* Include multiple vegetables for fibre
* Control fat intake during insulin-raising meals
* Eliminate added sugar and refined flours
The goal was never to eat less.
It was to remove the specific food combinations that block fat burning, while still allowing people to eat real, satisfying food.
Final Thought
If some foods seem to make you gain weight faster than others, you’re not imagining it.
Your body is responding exactly as it was designed to.
The solution isn’t more willpower.
It’s better metabolic signals.
Scientific References
- Simpson SJ, Raubenheimer D. The Protein Leverage Hypothesis. Obesity Reviews, 2005.
- Raubenheimer D, Simpson SJ. Protein leverage and obesity. Obesity, 2019.
- Hall KD et al. Ultra-processed diets cause excess calorie intake and weight gain. Cell Metabolism, NIH, 2019.
- Ludwig DS et al. The carbohydrate-insulin model of obesity. AJCN, 2021.
- Holt SHA et al. The insulin index of foods. AJCN, 1997.
- Te Morenga L et al. Dietary sugars and cardiometabolic risk. BMJ, 2013.
- Reynolds A et al. Carbohydrate quality and health outcomes. BMJ, 2019.
- Westerterp-Plantenga MS et al. Protein intake, satiety, and energy balance. AJCN, 2009.
