By Olivia Tarantino
Despite what their name implies, dietary fats won't make you fat. Well, unless you eat too much—or too little—of them.
You read that right. One of the most infuriating ironies of a low-fat diet is that going on one is actually more likely to make gain belly fat. And that's not the only negative side effect.
Dietary fats are an important nutritional component of a healthy eating pattern not only because they're essential for providing our body with energy, building healthy cells, and regulating hormones, but also because fat is required for the absorption of fat-soluble vitamins that boost immunity and maintain bone, eye, and skin health.
Although fats have gotten a bad rap over the past few decades, history is being rewritten, thanks to modern researchers reevaluating past data. For example, in April 2016, the journal BMJ published a re-evaluation of a 40-year-old study that initially concluded saturated fats cause high cholesterol and heart disease. The shocking truth? The exact opposite is true, and experts speculate an accurate analysis was never published because the results didn't support the firmly-held notion that saturated fat was bad.
Now, we're slowly piecing the real story back together. And experts are clearing up both the benefits that fats play in maintaining a healthy lifestyle, as well as the negative side effects we experience if we don't eat enough. Not sure if you're eating enough of the stuff? Read on to see the surprising things that happen to your body if your diet doesn't contain enough fat. And if you're looking to slim down, start with getting rid of these 40 Bad Habits That Lead to a Fat Belly.
1. You'll Be Hungry Often
When you eat less of one macronutrient (i.e. fats, carbs, and protein), you'll have to make up for the calories somewhere else. Those who eat less fat end up eating more carbs. The combination of eating more carbs and less fat can make you feel hungry all the time; here's why.
Your Blood Sugar Will Fluctuate Regularly
When you eat more carbs, you're also likely to eat more simple carbs—the rapidly-digested nutrients that can spike your blood sugar. If you aren't exercising, your body typically doesn't need all of this energy. A hormone known as insulin will store excess energy as fat and your blood sugar will plummet. A drop in blood sugar alerts your brain that you're hungry—again—even though you just ate. It's one of the 30 Reasons Why You're Always Hungry.
Fats Slow Absorption of Nutrients, Which Promotes Satiety
Studies published in The American Journal of Clinical Nutrition support the fact that consuming fat can help reduce hunger and impair food intake by increasing satiety signals and slowing digestion.
2. Your Heart Health Will Be At Risk
When a study sought to compare the clinical benefits of a conventional low-fat diet with the high-fat Mediterranean diet, the The New England Journal of Medicine study actually had to be stopped early because the Mediterranean diet participants reduced their risk of heart attack and stroke rate so much more than the conventional diet that it was deemed irresponsible to keep patients on the conventional diet. Find out why low fat diets put your heart health at risk below.
You Won't Reap The Protection from Monounsaturated Fats
When eaten in moderation, and in places of trans fats and saturated fats, monounsaturated fats can have a beneficial effect on your heart. According to a review of current studies published in the journal Nutrients, high-monounsaturated-fat diets increase levels of "good" HDL-cholesterol and decrease levels of triglycerides, which the Mayo Clinic says corresponds with decreasing your risk of heart disease and stroke. Without monounsaturated fats in your diet, you won't reap their cardioprotective benefit or the fact that many foods with this macronutrient make it on our list of 26 Foods That Melt Love Handles.
You'll Eat More Sugar
Before 2016, people believed that reducing intake of saturated fats was the most effective way to decrease your risk of coronary heart disease (CHD). That's not the case. According to a Progress in Cardiovascular Diseases study published this year, sugar is actually to blame. The authors concluded that sugar consumption, particularly refined added sugars (and even more specifically, fructose), is a greater contributor to CHD than saturated fats.
3. Your Body Can Become Chronically Inflamed
Although inflammation is a natural immune response that protects your body from colds and injuries, it's possible to switch your body into a chronic state of inflammation. This can cause weight gain, joint pain, drowsiness, skin problems, and a host of diseases from diabetes to cancer. So how does a low-fat diet play a role in inflammation? Find out below.
You're Eating More Sugar
Like we said before, when you're not eating enough fat, you're likely eating more carbs. Here's the deal: Eating a high-carb meal that lacks digestion-slowing nutrients such as fiber, healthy fats, or protein can spike your blood sugar rapidly. (Overnight oats are full of carbs, but maintain their place on our favorite anti-inflammatory foods because they contain a fiber that's fermented into anti-inflammatory fatty acids in your gut.) Research has found that post-eating blood sugar spikes can increase inflammation due to your body's overproduction of inflammatory free radicals called reactive oxygen species (ROS).
You're Eating Fewer Anti-Inflammatory Fats
When you don't eat enough fats, you can't reap the rewards of healthy fats, such as polyunsaturated fats EPA and DHA. Found in abundance in fatty fish, these omega-3 fatty acids attack excess inflammation by increasing adiponectin—a hormone that enhances your muscles' ability to use carbs for energy, boosts metabolism, and burns fat—which ultimately decreases inflammation markers, according to a review in the journal PLoS One.
You Won't Reap the Anti-Inflammatory Benefits of Antioxidants Found in Healthy Fats
One of the main reasons the Mediterranean diet has been found to be an effective inflammation-fighting diet? Oleocanthal. It's not a fat, but an antioxidant compound found only in a fat: unrefined extra virgin olive oil. According to a review published in the International Journal of Molecular Sciences, this polyphenol reduces inflammation in a similar way that ibuprofen does: it prevents the production of two pro-inflammatory enzymes, COX-1 and COX-2.
You Won't Reap the Anti-Inflammatory Benefits of Fat-Soluble Vitamins
Previous research published in the Journal of Inflammation Research has found a correlation between vitamin D deficiency and increased levels of pro-inflammatory markers.
4. You Could Increase Your Risk of Cancer
Not eating enough fat may make you more susceptible to certain types of cancers.
Low-Fat "Diet" Foods Are More Likely to Contain Potentially Cancer-Causing Additives
Some people who choose to leave fat out of their diet are often drawn to "low-fat" diet foods. Unfortunately, these processed foods are likely to make up for the lost taste of fat by adding in more artificial flavors and harmful additives. One of those additives, polysorbate 80, is a synthetic emulsifier added to foods to keep their ingredients from separating. It's often found in low-fat diet foods—like these diet ice creams—because fat naturally acts as an emulsifier, and manufacturers had to find a chemical replacement. Unfortunately, a recent study by Georgia State University researchers found that this additive may cause cancer by creating the ideal gut conditions for colon cancer cells to flourish.
High-Carb Diets Create Cancer-Causing Free Radicals
Again, if you're not eating enough fat, you're likely eating too many carbs. Eating a high-carb meal can cause spikes in your blood sugar, which we previously mentioned can create free radicals. According to Lisa Hayim, MS, RD, and founder of The WellNecessities, these "free radicals lead to oxidation of your cells and DNA, and they can cause enough damage to lead to cancer or other health conditions."
5. You May Develop Vitamin Deficiencies
Four vitamins—vitamins A, D, E, and K—are fat-soluble, rather than water-soluble. That means these essential micronutrients are only absorbed into the body once they're dissolved in fat globules. (It's why we always recommend some olive-oil-based dressing on your salad.) Once they're distributed throughout the body, the vitamins are then stored in the liver and fatty tissue for long-term use. When people don't eat enough fat, they may become deficient in these fat-soluble vitamins that play varying roles in maintaining proper bone, eye, and skin health.
6. Your Immune System Can Suffer
While Tufts University researchers found that a high-fat diet (around 38 percent fat) can impede an effective immune response, that doesn't mean you should cut fats from your diet entirely.
Fats Are An Important Building Block in Immune Response
According to a paper published in the journal Trends in Immunology, fatty acids are an important source of energy for T-cells, a type of white blood cell that plays a central role in maintaining a highly-functioning immune response.
Dietary Fat Helps You Absorb Vitamins That Play A Role In Immunity
Additionally, if you cut your fat intake too much, you might not be able to absorb fat-soluble vitamin E, which researchers from Tufts found to enhance the function of immune cells and help ensure health immune function as we age. Vitamin D, another fat-soluble vitamin, has also been implicated in helping your body fend off colds. Additionally, two essential fatty acids (those you can only get from your diet)—omega-3s and omega-6s—play important roles in the proper functioning of the immune system.
7. You'll Put Your Mental Health At Risk
High-Fructose Diets Damage Hundreds of Genes in the Brain—Fats Reverse This Damage
The typical American diet is full of sugar. In fact, the Department of Agriculture estimated that Americans consumed an average of 27 pounds of high-fructose corn syrup in 2014. That's bad news because a new study out of UCLA found that high-fructose diets can turn off hundreds of genes in your brain. Even worse news? If you aren't eating enough fat, you won't be consuming the omega-3 fatty acids that were found to help reverse this damage.
Fats Protect Your Brain and Help Preserve Memory
A large-scale study on older populations published in the journal Neurology found that adhering to a Mediterranean diet that was rich in healthy fats like olive oil, nuts, and fish can help preserve memory and reduce the risk of cognitive impairment.
Inflammation Harms Your Gut Health, Which Influences Depression and Anxiety
Since you'll be eating more carb-laden foods that cause inflammation, you'll begin to damage your gut health. Mounting scientific evidence is showing that the composition of our gut plays a critical role in influencing cognitive behaviors and emotions such as anxiety, depression, stress, autism, learning, and memory through what's known as a "gut-brain axis," according to a review in the Journal of Agricultural and Food Chemistry. In fact, an astounding 95 percent of your happy hormone serotonin is made and stored in your gut. Who knew? The issue is that inflammation damages your gut health, and thus, can increase feelings of anxiety, depression, and stress.
More Cortisol Means More Stress
Elevated blood sugar levels have also been associated with elevated cortisol levels: the hormone that stores fat and causes you to feel stressed.
Fats Build Brain Cells; Without it, You May Feel Like Your Brain Is In a Fog
Fats act as structural components of not only cell membranes in the brain, but also of myelin: the layer of fat that surrounds each nerve fiber and enables your brain neurons to carry messages.
8. You'll Lack Endurance
Feeling like your lifting routine post elliptical session is particularly arduous? You know that carbs are key to providing your body with a quick source of energy during your workout, but they're not the only macro you need to be worrying about if your exercise routine exceeds 20 minutes. According to Leah Kaufman, MS, RD, CDN, while your body will burn through carbs first, "Once the carbs have been used up, the body can start using stored fat for fuel." So while you might be able to push through a short elliptical session depleted, your body needs energy from fat to get through a longer cardio or lifting session. Without eating enough fat, your exercise routine will be cut short.
9. Your Physical Appearance May Suffer
You'll Have Dry, Flaky Skin From Missing Out on Fat-Soluble Beauty Vitamins E and K
Mono- and polyunsaturated fats keep your cells and skin happy. Two vitamins—vitamin E and vitamin K—require fat in order to be absorbed by your body. Without them, your skin may suffer. "Vitamin E helps to rehydrate the skin and reduces dry and rough skin," says Tanya Zuckerbrot, MS, RD. As for vitamin K, this micronutrient also plays a role in maintaining healthy skin and is believed to prevent wrinkles and premature aging.
You May See More Inflammatory Skin Conditions
Omega-3 fatty acids work to decrease inflammation. "Omega-3s may reduce the presence of acne and other skin conditions as well," explains Kathy Siegel, RD, CDN, who notes that research has shown an increase in dietary essential fatty acids can also prevent both chronological and sun-damaged induced signs of aging.
High-Sugar Diets Result in the Formation of Age-Accelerating Compounds
A review published in the American Journal of Clinical Nutrition concluded that a high sugar intake is associated with the formation of advanced end glycation products (AGEs, which, coincidentally accelerate aging). When your body has elevated levels of glucose and fructose (two sugar molecules), these excess sugars can link haphazardly to proteins, producing these compounds known as "AGEs." Studies have found that two of the proteins that are particularly targeted are collagen and elastin—two compounds that keep your skin tight and plump.
10. Your Hormones Will Be Out of Whack
Women May Lose Their Menstrual Cycle
Fats help regulate the production of sex hormones. Case studies of young teenage girls who didn't eat enough fat have found they experience delayed pubertal development. Additionally, post-puberty women may experience a loss of period because of a low body-fat percentage. (P.S. Fat isn't the only thing that affects your period; so do these 14 Best and Worst Foods For Your Period.)
Too Much Sugar Causes Metabolic Issues
When your diet is high in carbs and sugar, it can cause hormonal imbalances, "including elevated levels of cortisol, glucose, and the increased need for insulin," explains Lisa Mikus, RD, CNSC, CDN. "This can lead to central abdominal obesity (aka belly fat) and metabolic disturbances like diabetes."
11. You'll Likely Gain Weight
If you're looking to lose weight and keep it off, a low-fat diet isn't your best bet. Omega-3s reduce belly fat storage by tackling inflammation head on, and fats, in general, improve satiety and prevent you from overeating blood-sugar-spiking refined carbs.
The 2015-2020 Dietary Guidelines for Americans recommend consuming less than 10 percent of calories per day from saturated fats, or about 22 grams for those following a 2,000-calorie diet. Because the Dietary Guidelines does recommend a healthy eating style can contain up to 35 percent of total calories per day from fat, up to 25 percent of your total calories, or roughly 56 grams of fat should come from polyunsaturated fats—like fish, chia seeds, and flax seeds—and monounsaturated fats—found in nuts, olive oil, and avocados. For more good-for-you fats, check out these 20 Healthy Fats That Help You Get Thin.