This might seem obvious to a lot of people now—but 20 years ago this concept was revolutionary: carbs—not fat—cause people to store fat. There are a zillion websites and medical journals that explain this better than I can, but here’s the basic breakdown:
Calories are how we measure energy provided to your body. You can get energy from anything with calories (basically any food). That energy comes from carbs, fat, and/or protein. But each of these sources plays a very different role. In order to understand why and how carbs can make you fat, you need to understand the pros and cons of getting your energy from carbs vs. fat vs. protein:
The Difference Between Carbs, Fat, And Protein
- Carbohydrates are a highly efficient source of fuel because your body requires less oxygen to burn carbs than it does protein or fat. During high-intensity exercise, when your body can’t process enough oxygen to meet its needs, carbs are the go-to energy source.
- Fat is a highly-concentrated, slow-burn fuel. It has more than twice the energy per gram as carbs or protein. It is the preferred fuel source for moderate-intensity exercise and at-rest activity. In many cases, fat will contribute 50 percent or more of the energy your body needs for day-to-day activities. Fat is the ideal energy source for long-duration workouts.
- Protein is typically used to help repair and build muscle and other tissue in your body. Protein is a very low-quality energy source but can be used in an emergency if your body isn’t getting enough energy from carbs or fat. In a situation where you’re not feeding your body enough carbs or fat to produce the energy it needs, your body will either use the protein in your diet or start burning its own muscle to get a low-quality energy source.
(Side note: This is why you can’t safely lose more than about 2 pounds per week. Your body isn’t capable of burning fat any faster than that—and if you are losing weight at more than two pounds per week, those pounds are coming from muscle, not fat.)
To summarize, Carbs are your most efficient fuel source providing shorter, stronger bursts of energy. Fat is your slow-burn energy, it is the day-to-day stuff needed to run normal functions. Protein is something you never want to use as an energy source.
The Impact of Fat & Carbs on Blood Sugar
Your body’s energy can be measured by checking the glucose levels in your blood. Diabetics do this all the time. If you’re serious about learning how foods affect your body, you might consider buying a glucose meter yourself.
Fat in your diet will produce a slow, steady, level of blood sugar. This is great for normal, day-to-day activities. It’s the ideal energy-source for sedentary activities. Carbs, on the other hand, will provide a short-term spike in blood sugar to fuel a need for quick energy. Think of it like a turbocharger. They’re great for fueling high-intensity exercise. If you’re breathing heavy, carbs are the fuel you want.
All Carbs Are Not Created Equally
Some carbs will cause a MASSIVE spike in your blood sugar, and some will only cause a minor spike. It really depends on how complex the carbs are.
Simple carbs (like sugar, white wheat, etc.) are simple for your body to process. The entire result of those calories is converted straight to blood sugar energy. Simple carbs cause instant, massive spikes in energy (think sugar rush) that usually result in an energy crash causing your body to crave more of the same.
Complex carbs (clean carbs, as most people call them) provide a longer-term, sustained release of energy. Complex carbs (like whole grains) require a lot of extra work for your body to process; they result in a much more sustained and controlled blood sugar increase.
In other words… Simple carbs: bad. Clean carbs: good.
Examples of Simple Carbs (Dirty Carbs): apples, oranges, bananas, sugar, white bread, and white rice.
Examples of Complex Carbs (Clean Carbs): beans, whole wheat, oatmeal, brown rice, carrots, barley, and bran.
The Glycemic Index
Fortunately, there’s a simple way to tell whether a carb is clean or dirty—Introducing… the glycemic index! One of many new tools in your weight-loss arsenal. Essentially, the higher the food is on the index, the more likely it is that eating that food is going to send you in the wrong direction. Foods below 55 on the glycemic index are considered low.
So what happens if you eat dirty carbs that spike your blood sugar levels?
Well, it’s not necessarily a bad thing (if you need the energy), in fact, many marathon runners will eat huge quantities of sugar during their races. I eat a banana before every run because I want that short-term energy burst and I put it to good use. But most of us spend all day every day sitting around. We eat a carb-heavy meal (like pasta, pizza, or a sandwich with white bread), and then we sit back down at our desk and go back to work. (So unless you’re an athlete, or you spend a fair amount of time at the gym, simple carbs have no place in your life).
Dirty Carbs Make You Fat—FAST
When your body has excess energy that it has no need for (e.g. you eat the simple carbs, your body produces blood sugar, but you don’t do anything active after you’re done), any food sitting in your stomach will get converted to fat. Your body says, “Well, we’ve got all this food and no need for this extra fuel… I guess we will store it for later!” and thus, you gain weight. Oversimplified? Perhaps. But this is a simple way to visualize it.
Put another way, if you eat simple carbs but don’t use the resulting short-term bursts of energy, your body will use that energy to store the food sitting in your stomach as fat.
So you can see why foods like donuts or pizza are the perfect storm for weight gain. Donuts are loaded with carbs AND fat. So you eat the donut, which produces a blood sugar spike, but then sit on the couch and watch TV. Your body responds by taking all the fat from the donut and storing it for later. So even though that donut was only 400 calories, almost 100 percent of it goes straight to your hips. The same goes for that pizza.
This is also where a lot of people screw up from the very beginning. You know how we’ve always been told that “eating a lot of fruits and vegetables is the key to weight loss” Yeah right. Guess which foods are extremely high on the glycemic index? Most fruits and many vegetables. Eating pineapple, oranges, and potatoes is the perfect recipe for weight-loss failure.
This is just more proof that not all calories are created equal. If your calories come from sugar and fat at the same time (i.e the donut example), you’re far more likely to store those calories as fat than if those calories had been from different sources at different times of the day.
Simply put, I would avoid any and all foods that are high on the glycemic index unless you’re intentionally using them as a short-term energy source before or during a workout. This means no more white bread, avoiding most fruits, swearing off fruit juice, and—I hope it goes without saying—but deleting any and all sugar from your diet.
Note that “If It Fits Your Macros” (IIFYM) says you can eat whatever you want as long as it fits. However, IIFYM doesn’t distinguish between low-glycemic carbs and high-glycemic carbs. It’s your job to make smart choices in this respect.
Do You Even Need Carbs?
If you’re trying to lose weight with minimal exercising, I would consider cutting the carbs to an absolute minimum. You don’t need them, and fat is a much more efficient energy source for sedentary activity. Adjust your IIFYM ratios for a low-carb/ketogenic approach to dieting (perhaps 15 percent carbs, 20 percent protein, and 65 percent fat).
Cheating is disastrous when it comes to carbs.
One warning. Simple carbs create cravings for themselves. In your first 3-4 days of eating this way, you’re going to CRAVE simple carbs and sugar. You’ll CRAVE bread. You’ll CRAVE your favorite sugary snacks. But I promise if you stick to it and don’t give in (and resist the temptation to cheat), after a few days those cravings will go away and you won’t miss them. You may find that your body reacts negatively to not being fed simple carbs. You may even have flu-like symptoms for a few days and think that’s a sign your body isn’t getting the calories it needs. Total crap. Keep at it. Your body is detoxing. It doesn’t last long.
People who are constantly battling cravings or constant demands for sweets are typically cheating every so often. Those cheats are catastrophic. They ignite cravings. Be strong. It might only be 50 calories, but the blood sugar spike that results will reignite cravings. It’s not worth it.