Well, it’s officially the New Year, and for millions of Americans, that means that the annual tradition of trying diets, counting carbs, and trudging to the gym is fully underway. But after years of setting, bravely attempting, and then forgetting this infamous New Year’s Resolution, I’m sure many of you find weight loss as frustrating a goal as ever. I sure do.
It makes one wonder: how exactly does weight loss even work?
To get started, I’m sure you’ve all heard the familiar phrase: “A calorie is a calorie.” Your body uses up a certain amount of energy every day, measured in calories, to carry out its basic functions and power any physical activity. You gain energy from the total calories of the food you eat. Your body balances the net input or output, and either stores excess energy throughout the body in fat reserves or breaks down fat in the body to make up any energy deficit.
So, to start burning off those energy reserves and lose weight, all you have to do is have a net caloric deficit. Simple, right?
Unfortunately, it’s not quite that easy. Just like the promises we make about going to the gym, reality can be a lot more complicated. For starters, your body doesn’t directly turn food into energy.
Instead, as food is broken down in digestion, different nutrients get processed in different ways. Carbohydrates are broken down into simple sugars, typically glucose and fructose, and sent to the liver where they are stored as glycogen as part of the insulin feedback system. Proteins are broken down, absorbed, and shipped throughout the body, going wherever they’re needed to build new protein. Fat is dissolved and then enters the blood stream through the lymphatic system, where it gets stored by fat cells throughout the body.
Interestingly, fat cells don’t divide and grow in the same way normal cells do, instead just typically increasing in size, with the number of cells staying pretty constant. Though this doesn’t change the calorie value of any nutrient (one calorie of fat is the same amount of energy as one calorie of protein), it does change how your body treats that calorie.
For starters, your body uses the most readily available energy in the form of broken-down carbohydrates first before trying other energy sources. After exhausting easily available energy, it will then finally reach into energy reserves such as fat.
When your body uses more energy than it takes in for prolonged periods of time, it goes into energy saving mode, entering ketosis. That’s where the keto diet comes in: by eating a diet low in carbohydrates and high in proteins and fats, which are “harder” forms of energy for your body to harness, you can get your body to begin using those energy stores more quickly.
But putting your body into the state of ketosis can initially cause stress—your body thinks it’s in an emergency situation where it doesn’t have access to normal carbohydrate nutrients, leaving you feeling lethargic as your body cuts costs in other ways. The balance of different nutrients in your diet can lead to significant impacts in the hormone pathways responsible for your hunger and your brain’s cravings for different foods.
Another important consideration is the energy content of different nutrients. A calorie may be a calorie, but there are big differences in how full you’re left feeling after eating different nutrients. Fat contains 9 calories per gram while proteins and carbohydrates contain about 4 calories per gram, meaning a smaller meal heavy with fat could easily have many more calories than a larger one.
While fat in moderation can help you feel full and is an important part of a healthy diet, it can quickly takeover your caloric intake. To put things into perspective, a single Snickers bar has the same number of calories as 1.4 pounds of broccoli. How full you physically feel has a lot to do psychologically with being able to lose and keep off weight, so even though two meals may be calorically equivalent, the healthier option will be much more beneficial for your weight loss goals.
All in all, just like many things in life, there is no free lunch when it comes to weight loss—at least not one that’ll get you to your New Year’s goals without cutting back on your diet and hitting the gym. The human body is remarkably good at managing its resources and conserving energy, which means there’s a lot of work ahead for all of us trying to work off all those desserts from the holidays.
So ignore the latest diet trending on social media. The best and healthiest way to lose weight is by combining regular exercise with a balanced diet, for a consistent, maintainable caloric deficit. That way, not only will you lose weight, but more importantly, you’ll be healthier, happier, and scientifically much more likely to keep the weight off.
Will 2019 finally be the year we manage to check this New Year’s resolution off the list? I guess we’ll find out.
(Dr. Yadav Pandit is an experimental nuclear physicist currently working at Allen Community College as a physical science instructor. He writes a column of general interest in science for The Register.)
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