Popular diets are constantly changing, and it's not unusual for two diets to directly oppose each other. Low-fat and low-carb diets have been extremely popular over the years with no clear favorite emerging. If you decide to try a low-carb diet, you can make it work for you, but you have to know the side effects.
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How Low Should You Go?
Low carb is a very general term that simply means eating less than your daily recommended value of carbohydrates, which is about 130 grams, according to an article from the University of Louisville. An extreme low-carb diet is 20 to 50 grams of carbs.
There's no definition set in stone for low-carb diets, and some people believe that, as long as you consume less than 45 percent of your calories per day from carbs, you're eating a low-carb diet. However, popular forms of low-carb eating, like Atkins and the keto diet, are typically below 50 grams of carbs per day.
How to Lower Carbs
To lower your carb intake, it helps to track what you eat throughout the day. Use a food-tracking app like MyPlate to see how many grams of carbs you eat in a typical day. Then, slowly start to cut back.
Most people take out big sources of carbs from their diet like pasta, oats, rice and potatoes. When you remove these sources of carbs, you should notice a large drop in your daily carbohydrate intake. Sugary cereals, desserts and soda are also big sources of carbohydrates.
Read more: Negative Side Effects of a Low-Carb Diet
As you lower your carbs, you have to eat more fat and protein to balance out your calorie intake. Usually, meat and seafood are the best sources of fat and protein. Low-carb diets are easier for meat eaters, but harder for vegetarians, since most vegetables and fruits contain carbohydrates.
Adjusting to a Low-Carb Diet
Once you balance your diet and figure out your favorite low-carb, high-fat and high-protein foods, your body will start to adapt to your new low-carb lifestyle. At first, you might notice a drop in energy. That's because your body is used to having sugar running through your bloodstream after every meal.
Most organs, muscle tissue and your brain run on carbohydrates regularly, so your body has to revert to using fat for energy. This process is called ketosis, because your body is producing ketone bodies that can do the same job as glucose, but are actually made from fat, according to an article from Harvard Health.
Low Carb for Weight Loss
That doesn't necessarily mean that you burn more fat on a low-carb diet, however. Burning fat just means that it's your preferred fuel source. In fact, a 2018 study published in the Journal of the American Medical Association showed that subjects who ate low-carb diets didn't lose any more weight than people eating low-fat diets.
The key to this study is that each group ate the same amount of calories. That's the most important thing when it comes to losing weight. The macronutrients you eat are secondary.
Low-Carb Diets Reduce Hunger
But it remains that people keep eating low-carb diets because they reduce hunger and make you less likely to overeat. A 2016 study published in Nutrition, Metabolism and Cardiovascular Diseases showed that eating a low-carb diet reduces your hunger, which naturally cuts your calories and helps you lose weight.
Benefits for Diabetics
Diabetics also benefit from low-carb diets. In both Type 1 and Type 2 diabetes, your body may have trouble regulating blood sugar levels. If your body can't naturally lower blood sugar levels, you may need to take medication like injectable insulin or metformin.
Low Carb Lowers Blood Glucose
While it's not a replacement for taking drugs, eating a low-carb diet can naturally lower your blood glucose levels. When you eat carbohydrates, your digestive system breaks it down into simple sugar, otherwise known as glucose. Then it's sent into your bloodstream where your muscles, liver or other organs use it. You can also convert it to fat.
Insulin signals your body to pull blood sugar out and store it. People with diabetes either don't make enough insulin or they can't use the insulin they do make, which is why they may have to take medication. Eating a low-carb diet prevents blood sugar levels from rising too high, which makes insulin less important.
A 2015 study published in Nutrition found that low-carb diets lowered blood glucose even if the subjects didn't lose weight. They also found that some people were able to reduce and even stop taking their diabetes medication. This is incredibly useful because some medications cause unwanted side effects.
Low-carb diets aren't inherently dangerous, but there are side effects. Athletes may notice a decrease in performance. Some cardiovascular risks, such as high cholesterol, can increase when you eat low carb.
Watch Your Cholesterol Levels
While eating more high-fat and high-protein food makes you feel full and helps you cut calories, it might raise your LDL cholesterol. Animal products, especially meat and dairy, are particularly likely to raise your cholesterol levels. A 2016 study from the British Journal of Nutrition shows that low-carb diets can raise cholesterol levels even if you're losing weight.
There are two kinds of cholesterol: HDL and LDL. HDL cholesterol is considered healthy, and you actually want more of it in your body. LDL is considered bad, and if you have over 130 milligrams per deciliter, it's considered a risk factor for heart disease, according to an article from Medline Plus.
If you're starting a low-carb diet and want to know how it affects your cholesterol levels, you can go to your doctor for a blood test to monitor your LDL levels.
Digestive Issues to Watch For
Your digestive system might not like eating high fat and high protein all the time. Low-carb diets help with weight loss because they make you feel full, but the extra work your digestive system has to do can take its toll. Since high-fat and high-protein foods are more difficult to digest, low-carb diets can cause stomach pain.
A guide to the ketogenic diet for pediatricians published in Healio outlines some of the dangers of the keto diet. Ketogenic diets are very high in fat, moderate in protein and very low in carbohydrates. To eat a keto diet, you should have only about 5 percent of your daily calorie intake from carbohydrates, according to an article from the Cleveland Clinic.
The higher your fat intake is relative to protein, the more likely you are to experience digestive issues, according to the article from Healio. Some people even experience stomach pains and need to vomit from the high amount of fat, although this isn't a common side effect of the diet.
There's also a risk of constipation since the keto diet is low in fiber. Fiber is a form of carbohydrate that your body can't readily digest. Fruits, vegetables and oats are all high in fiber, but they also include carbohydrates, so you might not be able to eat them and stick to the keto diet.
Read more: What Are the Dangers of Ketosis Diets?
Higher Risk of Kidney Stones
Kidney stones are also a concern of high-fat diets. The risk for kidney stones on the keto diet are between 2 and 6 percent, but can be as high as 25 percent after six years on the diet, according to the article from Healio.
Kidney stones can be incredibly painful. They're small collections of minerals and salts, and if they break off and float down your ureter, they can block the flow of urine into the bladder.
Missing Vitamins and Minerals
Cutting out carbohydrates means you're leaving entire groups of food behind. You'll lose foods like whole grains or oats and only consume a limited amounts of fruit and vegetables. When you cut out food groups like these it's harder to get all vitamins and minerals in your diet.
The article from Healio points out that, if you're not eating enough vitamin D and calcium, your skeleton may suffer. That's why some growth deficiencies have been reported in children on the keto diet. For adults, this can increase the risk of osteoporosis.
Low Carb Can Hurt Performance
Carb loading is an infamous precompetition strategy for athletes. The day before a big race or sporting event, it's not uncommon to see an athlete wolfing down a plate of pasta, rice or potatoes. Carbohydrates are the preferred source of fuel for your muscles, especially for short-burst activities. Your body can convert muscle-stored glycogen to energy faster than it can convert fat.
When you lower your carb intake, your muscles have to rely more on fat than stored glucose. This can hurt performance, according to a 2015 study published in Sports Medicine. The study looked at distance runners competing in an event lasting up to three hours. The researchers found that even three hours into the event, they were still running mainly on carbs.
The researchers also found that the amount of carbs the athletes stored was a big factor in their performance. As the athletes ran out of carbs, they seemed to hit a wall and performance slowly dipped.
Eating a low-carb or keto diet can hurt your performance, especially when you first start the diet. As your body gets used to storing fat instead of glucose for energy, your performance can normalize. However, it's not uncommon to experience weeks or months of decreased performance before you bounce back, according to an article from the National Strength and Conditioning Association.
Brain Function Without Carbs
Your brain runs on glucose if you have carbs in your diet. If you don't, your body produces ketone bodies that your brain can use as fuel. However, when you switch to a low-carb diet and your blood sugar levels drop, you might not be as sharp as normal.
Your memory and mood might not be the best indicators of your health while cutting back on carbs. There are many factors that go into your energy level and mood for the day. Perhaps you're under stress at work or didn't sleep well. That can skew energy levels and how you feel.
A 2017 study published in The FASEB Journal shows that a ketogenic diet can actually increase your ability to react quickly. There's still not enough evidence on the subject to say whether carbs hurt or help your memory and problem-solving skills, but it's safe to say that no clear link exists yet.
- University of Louisville School of Medicine: Low-Carb Diets
- JAMA: Effect of Low-Fat vs. Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion
- British Journal of Nutrition: Effects of Low-Carbohydrate Diets v. Low-Fat Diets on Body Weight and Cardiovascular Risk Factors
- Nutrition: Dietary Carbohydrate Restriction as the First Approach in Diabetes Management
- Medline Plus: LDL: The "Bad" Cholesterol
- Cleveland Clinic: What Is the Keto Diet (and Should You Try It)?
- Urology Care Foundation: What Are Kidney Stones?
- Sports Medicine: Carbohydrate Dependence During Prolonged, Intense Endurance Exercise
- NSCA: How Low Can You Go? Considerations for Low-Carbohydrate Diets
- The FASEB Journal: The Effects of a Ketogenic Diet and Exercise Interventions on Cognitive Function
- Healio: The Ketogenic Diet: A Practical Guide for Pediatricians
- Harvard Health: Ketogenic Diet: Is the Ultimate Low-Carb Diet Good For You?