7 Surprising Side Effects of a Low-Fat Diet Worth Knowing

by Chelsey Amer, MS, RDN, CDN · February 22, 2021

Chelsey Amer, MS, RDN, CDN, investigates what happens when you don’t eat enough fat. Read up on the side effects of a low-fat diet to rethink your approach to this necessary macronutrient.

If the low-fat craze of the 1990s influenced your comfort to eat (or not eat) fat, let’s clear something up: Eating fat doesn’t make you fat! In fact, it’s widely accepted that healthy fats are important for your well-being. Yet still, as a registered dietitian, I see clients every day who avoid fat due to fear of gaining weight.

Before we get to the side effects of a low-fat diet, let’s first look at the benefits of eating healthy fats and how much you should eat per day.

Benefits of Healthy Fats

To begin, there are many healthy high-fat foods you can include in your diet, such as:

  • olive oil
  • avocados
  • olives
  • nuts + seeds
  • fatty fish

Among other things, benefits of healthy fats include:

  • support for heart health
  • a stable mood
  • glowing skin
  • balanced hormones
  • proper vitamin absorption

Conversely, opting for low- and no-fat products—like zero-percent fat Greek yogurt or powdered peanut butter—means you’re missing out on the many health and beauty benefits of healthy fats.

That said, not all fats are created equally.

Woman cutting into salmon avocado toast with a poached egg, a healthy high-fat meal that packs many health and beauty benefits

How much fat should you eat per day?

The Dietary Reference Intake (DRI) for fat is 20 to 35 percent of your daily calories.

However, according to the Dietary Guidelines for Americans, only 10 percent or less of that quota should come from saturated fat.

7 side effects of a low-fat diet

For starters, when you skip fat in your meals, it’s harder to:

If you’re still wary of adding fats to your meals, the potential side effects of a low-fat diet may change your mind.

1. Flaky, Dry Skin

Did you know that fat is an important component of skin cell membranes?

According to the American Academy of Dermatology, you shed 30,000 to 40,000 old skin cells daily. Your body constantly makes new ones, and it’s important that it has enough fat to do so. This is especially significant because fat helps maintain the skin barrier, locking in moisture and protecting your skin from irritants.

However, it’s not enough to simply lather yourself in lotion from head to toe. You need to eat fat to nourish your skin cells from the inside out.

Specifically, consuming essential fatty acids—found in fatty fish, nuts, seeds, high-quality vegetable oils, and more—can help mitigate the inflammatory response in your skin, reducing redness.

Aim to consume fish twice weekly, as well as nuts, seeds, avocado, and olive oil for glowing, moisturized skin.

Close-up of man's shoulder with flaky, dry skin due to sunburn

2. Increased Sensitivity to Sunburn

You’re likely aware that it’s important to apply sunscreen daily—especially when you’re outside. But did you know that what you eat impacts your ability to burn, too?

Researchers have found that essential fatty acids (like omega-3s) can help reduce cellular stress and inflammation caused by UV rays.

Though we need more research on this point, you can start protecting your skin from within by adding omega-3-rich foods like fatty fish, nuts, and seeds to your shopping cart. And yes: Sunscreen is still necessary!

3. Mood Imbalances

Since your brain is 60 percent fat, it’s no wonder that potential side effects of a low-fat diet include brain fog and moodiness.

Studies consistently show that low-fat diets can increase anger, irritability, and low mood due to changes in serotonin, a feel-good brain chemical. Furthermore, researchers found that women following a low-fat diet over an extended period of time reported greater levels of stress.

Essential fatty acids, like omega-3 and omega-6 fatty acids, are well-known to support mental health. On the other hand, low omega-3 fatty acid intake is associated with mood imbalances. That’s why healthy high-fat nuts, seeds, fatty fish, and even chocolate are often considered some of the best brain foods.

4. Hormone Imbalances

Many key hormones in your body are made from fat. For this reason, a low-fat diet can interfere with proper hormone production and function.

Plus, certain sex hormones—including estrogen and testosterone—rely on fat. This means that ultra low-fat diets can interfere with proper hormone balance, potentially leading to:

Try this chocolate avocado mousse recipe for a delicious dose of healthy fats from avocado.

5. Constant Hunger

Feel hungry around the clock? You may want to switch up your diet to ensure you’re eating enough fat.

Out of the three major macronutrients (carbohydrates, protein, and fat), fat digests the slowest. It takes longer to digest and absorb fat from your food, meaning you can endure longer stretches free from hunger pangs.

However, it’s not just fat’s slower rate of digestion that keeps your hunger at bay. Hormones also play a key role in satiety. Yet another benefit of healthy high-fat foods is that they help turn off ghrelin (aka the hunger hormone), so you get the message to pause your food intake.

Hungry woman looking into fridge at night, who has cravings around the clock as a side effect of a low-fat diet

6. Poor Vitamin Absorption

Did you know that you need to eat fat to adequately absorb vitamins including A, D, E, and K?

For instance, eating vitamin K-rich dark leafy greens without any source of fat will lead to less vitamin K absorption than if you added healthy fats—like oil-based dressing or avocado—to the mix.

That’s because vitamins A, D, E, and K are fat-soluble vitamins, meaning they require fat for better absorption in your body.

7. More Cravings

If you find yourself constantly grabbing highly processed, high-carb and high-sugar foods, you’ll be better off boosting your fat intake throughout the day.

Choosing healthy high-fat foods (like full-fat dairy over fat-free versions) can lead to greater satisfaction from food and therefore fewer cravings. Plus, adding healthy fats to your meals will better balance your diet, thus also curbing cravings.

The Bottom Line

Not only can a lack of fat in your diet lead to unpleasant side effects, but it can also throw off your nutrient balance. Take care to follow a well-balanced diet that includes a moderate amount of fat so you can feel your best.

Then, to go the extra mile and get personalized recommendations, it’s best to consult a dietitian.

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