How Appetite Dictates Weight Loss and Your Body Weight

Key Takeaways

1. Your appetite is controlled by your brain (the "hypothalamus"), which responds to hormone signals that either stimulate or suppress your appetite.
2. When you lose body fat, your body acts to mitigate further losses by increasing "hunger hormones" and decreasing "satiety hormones".
3. Palatable processed foods can bypass normal satiety signals. Poor sleep and stress further disrupt your appetite, making weight loss more challenging.

You’ve probably heard of having a “loss of appetite” or “controlling your appetite”, but far from simple hunger pangs, appetite is determined by your hormones, your brain wiring and your environment. Your appetite originally evolved to maintain survival; to ensure you have enough energy and nutrients to keep you alive. However, it now operates in a "food-abundant" world.

What is an "appetite"?

Appetite covers two separate (but interconnected) parts that control your eating behaviour:

1. "Hunger", which is the physiological need for food, is driven by energy depletion and hormonal signals.
2. "Satiation", which tells you when to stop eating. Think of it as the “I’m full” signal. “Satiety” signals maintain that feeling of fullness between meals and determine when you'll next seek food.

So you’re either full or hungry, or somewhere in between. Seems quite obvious, but these two systems work together through complex processes (called “feedback-loops”). The feedback loops involve your brain, digestive system, fat tissue, and several other hormones. Achieving (and maintaining) a healthy body weight requires addressing not just when to start eating, but also when to stop and maintain satiety levels over time.

Your brain: the central controller of your appetite

The part of the brain principally responsible for your appetite is the “hypothalamus”. Its role is to process the signals sent from different parts of your body and to coordinate the response (i.e., to eat or not to eat). It contains two parts: one that stimulates appetite and one that suppresses it. Both of these parts get their information from your hormones, the nutrient levels in the blood, and other parts of your brain. They process all this information together before adjusting your hunger and satiety settings. This entire system is basically done automatically for you and operates below “conscious awareness”.

How appetite hormones work

Multiple hormones regulate your appetite. For instance:

• “Ghrelin” hormone, produced by the stomach, increases before meals and stimulates hunger, but falls very quickly once you start eating.
• Contrast this with leptin, an appetite-suppressing hormone that is released from the fat tissue itself. Leptin doesn’t change as quickly as ghrelin, so it gives a longer-term perspective on how well you’re maintaining your appetite and energy levels.
• Glucagon-like peptide-1 (GLP-1), Gastric Inhibitory Polypeptide (GIP), Peptide YY (PYY) and Cholecystokinin (CKK) are four more “I’m full” (satiety) hormones, which are released by your intestines after you eat food.
• Neuropeptide Y (made in the brain) and cortisol (made in the adrenal glands) are two more "orexigenic" hormones that increase your appetite.
• Insulin, in addition to controlling your blood sugar levels, also has a critical role in regulating appetite.

All these different hormones have to work together and require precise timing and sensitivity to maintain a healthy appetite.

How appetite affects weight loss and body weight

Small disruptions in some of the processes that regulate your appetite can lead to changes in your body weight. For instance, when you start to lose fat, your body’s appetite systems actively defend against it by increasing the release of the “hunger hormones” and decreasing the release of the “satiety hormones”. Scientists call this response “metabolic adaptation”, and it partially explains why weight loss programmes are often not as straightforward as they sound.   

Whilst it may seem like it prima facie, your body isn’t trying to sabotage your new diet. It actually thinks it's protecting you. It doesn’t like sudden changes, irrespective of whether you need them or not. Losing a lot of weight, very quickly, can trick your body into thinking that you're starving. So it then initiates a hard-wired “starvation response”, which sends signals to increase food intake in the hope that you can restore the energy reserves. Understanding this physiological reality can help explain why sustainable weight loss requires working with, rather than against, your own appetite.

What derails your appetite

Your "food environment" can override natural appetite regulation processes, exploiting its natural vulnerabilities. Ultra-processed foods high in sugar, fat, and salt create eating behaviour(s) that bypass your normal satiety signals, directly stimulating the brain's reward system.

The near-unlimited availability and variety of food on offer can overwhelm our natural systems that control our appetites, which were designed for more food-scarce times. Historically, having a good appetite and a high motivation to find food was an advantageous evolutionary trait. However, today it is less of an advantage when thousands of different food options are available in unlimited amounts with just a few clicks.  

Sleep and large amounts of stress can also disrupt normal appetite regulation. Just one poor night’s sleep can increase your appetite. Too much stress can also increase hunger and shift preferences towards high-calorie, highly processed “junk” foods. There’s also a negative feedback loop here where: more stress leads to poorer sleep, and more poor sleep leads to more stress, and so on and so on, which exacerbates the problem further. 

Lastly, there is also an important distinction to make between "physiological" hunger (i.e., what food your body actually needs) and “psychological" hunger (i.e., what food your brain thinks your body needs). These are normally misaligned in people who struggle to control their body weight, and can be difficult to correct for some people. Scientists call this “metabolic scarring”. Therefore, rather than fighting your individual appetite profile, try to work with it where possible and tip the odds in your favour.