“I don’t” is experienced as a choice, so it feels empowering. “I can’t” isn’t a choice, is a restriction. 
In other words, the phrase "I don't" is a psychologically empowering way to say no, while the phrase "I can't" is a psychologically draining way to say no.

Words frame your sense of empowerment and control

Stress causes certain regions of the brain to release chemicals that can trigger mechanisms similar to the cravings you get from fat and sugar, so your brain feels the addictive call of fat and sugar and you’re pulled back to junk food.

Stress favors unhealthy eating

At the store, only go for the “outer ring” , where the healthy food usually lives: fruits, vegetables, lean meats, eggs, etc. These are items that grew or lived outdoors. That’s what you should eat. 
The aisles are where all of the boxed and processed stuff is placed.

The “Outer Ring” strategy for buying healthy food

Most people think that building better habits or changing your actions is all about willpower or motivation. But your environment has an incredible ability to shape your behavior. 
Nowhere is this more true than with food.

Building better habits means changing your environment

<ol>
<li>The sensation of eating the food: what it tastes like, what it smells like and how it feels in your mouth.</li>
<li>The blend of proteins, fats, and carbohydrates that it contains: junk food companies are looking for a perfect combination, that excites your brain and gets you coming back for more.</li>
</ol>

The reasons we crave junk food

<ul>
<li>Salivary response: the more a food causes you to salivate, the more it will cover your taste buds.</li>
<li>Rapid food meltdown: this tells your brain that you’re not full, even though you’re eating a lot of calories.</li>
<li>Calorie density. junk foods are designed to convince your brain that it is getting nutrition, but to not fill you up.</li>
<li>Memories of past eating experiences: When you eat something tasty, your brain registers that feeling and will bring it up in the future.</li>
</ul>

How craving are stimulated artificially

<ol>
<li>Use smaller plates. Bigger plates mean bigger portions.</li>
<li>Use tall, slender glasses instead of short, fat ones to drink less alcohol or soda.</li>
<li>Use plates that have a high contrast color with your food.</li>
<li>Display healthy foods in a prominent place.</li>
<li>Wrap unhealthy foods in tin foil and healthy foods in plastic wrap.</li>
<li>Keep healthy foods in larger packages and containers, and unhealthy foods in smaller ones.</li>
</ol>

Eat healthy using choice architecture

Healthy eating. It's something everyone knows they should do, but few of us do as consistently as we would like. The purpose of this guide is to share practical strategies for how to eat healthy and break down the science of why we often fail to do so.