Are Carbohydrates Really Making Us Fat?

For many Americans trying to get in shape, carbohydrates have become about as popular as cancer. How and why did this happen? After all, for hundreds of years our ancestors before us ate lots of carbs. Bread was a staple of the human diet for centuries and our ancestors rarely experienced obesity. So what’s going on? Obviously diets such as Atkins, Keto, Paleo, and other extreme low carb diets are partly to blame. But are carbs really the problem or is there more to it?


First and most importantly, all carbs are NOT created equal.

There are many different types of carbohydrate-containing foods, and they vary greatly in their health effects.

Although carbs are often referred to as “simple” vs “complex,” I personally find “whole” vs “refined” to make more sense.

Whole carbs are unprocessed and contain the fiber found naturally in the food, while refined carbs have been processed and had the natural fiber stripped out.

Examples of whole carbs include vegetables, whole fruit, legumes, potatoes and whole grains. These foods are generally healthy.

On the other hand, refined carbs include sugar-sweetened beverages, fruit juices, pastries, white bread, white pasta, white rice and others.

Numerous studies show that refined carbohydrate consumption is associated with health problems like obesity and type 2 diabetes.

They tend to cause major spikes in blood sugar levels, which leads to a subsequent crash that can trigger hunger and cravings for more high-carb foods.

This is the “blood sugar roller coaster” that many people are familiar with.

Refined carbohydrate foods are usually also lacking in essential nutrients. In other words, they are “empty” calories.

The added sugars are another story altogether, they are the absolute worst carbohydrates and linked to all sorts of chronic diseases.

However, it makes no sense to demonize all carbohydrate-containing foods because of the health effects of their processed counterparts.

Whole food sources of carbohydrates are loaded with nutrients and fiber, and don’t cause the same spikes and dips in blood sugar levels.

Hundreds of studies on high-fiber carbohydrates, including vegetables, fruits, legumes and whole grains show that eating them is linked to improved metabolic health and a lower risk of disease.


Research shows the most obviously persistent reasons for excessive carbohydrate and fat intake, and thus, the American obesity epidemic are:

💔 Labor-saving technological changes of the 20th century

💔 The industrial processing of food and with it the spread of fast-food eateries (To illustrate the spread of fast food culture, consider that White Castle, the first drive-in restaurant, was founded in 1921. McDonald’s started operation in the late 1940s, Kentucky Fried Chicken in 1952, Burger King in 1954, Pizza Hut in 1958, Taco Bell in 1962, and Subway in 1962.)

💔 The “More Is Better” American culture

💔 The rise of an automobile-based way of life

💔 The introduction of radio and television

💔 The increasing participation of women in the work force

💔 The IT revolution

These elements – taken together – virtually defined American society in the 20th century (Chou et al. 2008, Cutler et al. 2003, Hamermesh 2010, Lakdawalla and Philipson 2009, Offer 2006, Philipson and Posner 2003, Popkin, 2004).

Noteworthy in this regard is that the timing of the first accelerating phase after World War I among whites coincided with the spread of radios and automobiles, while the timing of the second accelerating phase of the 1950s cohorts among both blacks and whites coincided perfectly with the spread of television viewing and the spread of fast food consumption.


The human body needs all three types of carbs—sugar, starch, and fiber—to function well, according to the U.S. National Library of Medicine because they all get used by our bodies in different ways. (A quick note if you’re wondering, “Well, what about the keto diet?” Keto is indeed based on the fact that your body has a plan B when your carb intake is extremely low: ketosis, a process of converting fat into energy. But there are concerns about these kinds of diets, including the fact that you’re missing out on all the nutrients in carb-containing foods and the lack of data about the safety of fueling your body via ketosis long term.)

Now, broadly speaking, sugars and starches get broken down for energy usage and storage in our cells, tissues, and organs, per the U.S. National Library of Medicine. But fiber is the odd carb out: It actually passes through the body mostly undigested, but helps regulate things like digestion, blood sugar, and cholesterol.

The body is a little like a fancy car that only takes diesel gas, though. Its preferred form of fuel is a type of monosaccharide, or single sugar, called glucose. “Glucose is like our body’s currency for energy,” says Whitney Linsenmeyer, Ph.D., R.D., nutrition and dietetics instructor in the Doisy College of Health Sciences at Saint Louis University and spokesperson for the Academy of Nutrition and Dietetics.

Luckily, we don’t have to sit around guzzling glucose all day because the body is able to break down all the carbs we eat (save fiber) into glucose during the process of digestion and metabolism. It breaks carbs down into smaller and smaller pieces, with increasingly specialized steps along the way, until all that’s left is that readily usable form of energy, glucose, Linsenmeyer explains.


While all carbs follow the same track from our mouth to their final destination (cells throughout the body), the steps and length of time it takes them to get there depends on the structure of the molecules you’re starting with.

If you’re eating sugar—which, remember, is made up of single sugar molecules or two sugar molecules bonded together—it’s already pretty close to the body’s preferred form of glucose, so there’s not much work to be done. These small sugar molecules can be digested and absorbed into the bloodstream really quickly, which is why they’re the most rapid form of energy. (This is also why they are associated with a quick spike in blood sugar—your body absorbs all that glucose at once.) When you eat starch, the process of breaking it down into glucose happens over a longer period of time, because of its complex structure. (That’s why this type of carb provides a slower and steadier form of energy, and is less likely to cause blood sugar spikes.)

Amazingly, your body actually gets to work digesting some complex carbs before you even swallow them. “Your saliva produces something called salivary amylase, an enzyme that starts to break down [starches] as soon as they hit your mouth,” says Colleen Tewksbury, Ph.D., M.P.H., R.D., a senior research investigator and bariatric program manager at Penn Medicine and president-elect of the Pennsylvania Academy of Nutrition and Dietetics. (In fact, Tewksbury says, if you let a starchy food like white bread sit on your tongue for a while, it will start to get sweeter as the salivary amylase starts converting it into sugar.)

After you swallow those carbs, they get churned up with gastric juices in your stomach that contain various acids and enzymes. Then, the stomach passes this appetizing mixture on to the small intestine, where the real work of digestion happens, Tewksbury says. Here, more specialized enzymes and acids are introduced to break it down into even tinier bits.

Again, how long digestion takes depends on the kinds of carbs involved. Simple sugars have the greenlight to speed through the process we just described. If you’ve eaten something like candy or fruit juice, composed of simple sugars, there’s not much for your stomach and intestines to do, so this all happens really fast. Starches (and everything else) have to hang around for much longer at each point while they get broken down into smaller and smaller pieces, so the process is more gradual.


As carbs are converted into nice little bits of glucose, they become ready to enter the bloodstream. First, the glucose molecules travel from the small intestine to the liver via the portal vein, Linsenmeyer explains. The liver then dispatches most of that glucose throughout the body via the bloodstream.

Once it hits the bloodstream, some glucose will immediately get used by cells in need of energy—say, those in our brain or our muscles—thanks to the vital hormone called insulin. Insulin allows the glucose in our bloodstream to enter the body’s cells so it can be used for energy. When we eat carbs, the pancreas automatically secretes the perfect amount of insulin to help the cells use glucose and keep our blood sugar levels nice and steady. (This is why people with type 1 diabetes, whose pancreases don’t produce any or enough insulin, need to take insulin to keep their blood sugars in check.)

But we usually consume more carbs than we need at that exact moment. Rather than letting that excess glucose pile up in the bloodstream, the body stores it in a few ways.

A small amount of the glucose is converted into something called glycogen, our body’s special form of readily available “storage glucose” that get deposited in our liver and muscles as an emergency reservoir of energy to use when we need it, Linsenmeyer says—like when you go a long time between meals or go for a really long run, for instance. The rest of the excess glucose gets stored in our fat cells as body fat, again with the assistance of insulin. It can be accessed down the road when we have an energy deficit (i.e. using more calories than we’re taking in).

It’s worth saying that this is a pretty simplified look at what’s happening in our bodies when we eat carbs. There are a whole bunch of processes happening when we eat carbs (or any macronutrient), and scientists don’t even totally understand them all yet. “Our bodies are constantly spinning like 20 different plates at once every time we eat [food] to be able to break it down and utilize it,” Tewksbury explains. For example, there are a bunch of other hormonal secretions happening when we eat carbs or any food, but insulin is one of the most well-understood and useful to know about.

𝗦𝗢 ğ—•ğ—”ğ—–ğ—ž 𝗧𝗢 𝗢𝗥𝗜𝗚𝗜𝗡𝗔𝗟 𝗤𝗨𝗘𝗦𝗧𝗜𝗢𝗡— 𝗔𝗥𝗘 𝗖𝗔𝗥𝗕𝗦 ğ— ğ—”ğ—žğ—œğ—¡ğ—š 𝗨𝗦 𝗙𝗔𝗧?

Any food can cause weight gain if you overeat. Whether your diet is high in fat or high in carbohydrates, if you frequently consume more energy than your body uses you’re likely to put on weight.

In fact, gram for gram, carbohydrate contains fewer than half the calories of fat. Wholegrain varieties of starchy foods are good sources of fiber. Foods high in fiber add bulk to your meal and help you feel full.

But foods high in sugar are often high in calories, and eating these foods too often can contribute to you becoming overweight.

There’s some evidence that diets high in sugar are associated with an increased energy content of the diet overall, which over time can lead to weight gain.

𝗧𝗵𝗲 𝗯𝗼𝘁𝘁𝗼𝗺 𝗹𝗶𝗻𝗲 𝗶𝘀 𝘁𝗵𝗮𝘁 𝗰𝗮𝗿𝗯𝘀 𝗮𝗿𝗲 𝘀𝘂𝗽𝗲𝗿 𝗶𝗺𝗽𝗼𝗿𝘁𝗮𝗻𝘁—𝗮𝗻𝗱 𝘁𝗵𝗮𝘁 𝗼𝘂𝗿 𝗯𝗼𝗱𝘆 𝗱𝗼𝗲𝘀 𝗮 𝗯𝗮𝗻𝗴-𝘂𝗽 𝗷𝗼𝗯 𝗼𝗳 𝗽𝘂𝘁𝘁𝗶𝗻𝗴 𝘁𝗵𝗲𝗺 𝘁𝗼 𝗴𝗼𝗼𝗱 𝘂𝘀𝗲 𝘀𝗼 𝘄𝗲 𝗰𝗮𝗻 𝗴𝗲𝘁 𝘀𝘁𝘂𝗳𝗳 𝗱𝗼𝗻𝗲, 𝗯𝘂𝘁 𝗹𝗶𝗸𝗲 𝗮𝗹𝗺𝗼𝘀𝘁 𝗮𝗹𝗹 𝗳𝗼𝗼𝗱𝘀, 𝗺𝗼𝗱𝗲𝗿𝗮𝘁𝗶𝗼𝗻 𝗶𝘀 𝘁𝗵𝗲 𝗸𝗲𝘆!

1. Not All Carbs Are Created Equal. By Kathleen M. Zelman, MPH, RD, LD.
2. The Truth About Carbs.
3. The evolution of BMI values of US adults: 1882-1986. John Komlos, Marek Brabec. August 31, 2010

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