Here’s what happens to your body on the keto diet
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You’ve probably heard what proponents of the keto diet say: eat bacon and still lose weight! You’ll feel great! While this may sound tempting, there are some negatives to this way of thinking about the ketogenic diet. Misconceptions about keto can lead people to believe they can lose weight quickly while enjoying as much rich, fatty food as they like.
There’s more to the keto diet than that, Rodriquez says.
The body turns carbohydrate-rich foods, including fruit, vegetables, pasta and milk, into glucose, a type of sugar.1 Your body uses this energy to fuel everything you do — while you’re awake and while you’re asleep.2 Glucose, or blood sugar, is the body’s primary source of energy.3
“The goal of the keto diet is to dramatically reduce existing glucose in the body so that you trigger the use of fat as fuel instead. This is why it’s possible to lose weight on the keto diet,” Rodriquez explains.
This is what happens when you follow the keto diet:4
- Say goodbye to carbs (for the most part). You begin to add more fat and protein-packed foods into your diet and remove certain carbohydrate-rich foods. Your body will continue to use the glucose that’s stored in the liver for energy until it’s depleted.
- Insulin levels drop. After the body’s glucose stores are depleted, insulin levels (a hormone that helps the body’s cells to absorb glucose5) decrease.
- The body begins breaking down fat. When the body breaks down fat, it creates byproducts called ketone bodies that are used for energy instead of glucose.
- The body enters ketosis. Now that ketone bodies have built up in the blood, the body is efficiently burning fat as fuel. The keto diet aims to maintain ketosis by using fat rather than glucose as fuel, and as a result, may help you to lose weight.
Keto diet types
Not all keto diets are created equal. There are four main types, with different levels of fat, protein and carbs.
“A keto diet is typically high in fat and protein, but very low in carbohydrates,” Rodriquez says.
Common versions of the ketogenic diet include:6
- The standard ketogenic diet. This is the most popular version of the keto diet and usually contains 75% fat, 20% protein, and 5% carbs.
- The cyclical ketogenic diet. This version allows you to eat more carbs. In one example, you’d strictly follow the keto diet for five days and have two high-carb days.
- The targeted ketogenic diet. If you follow this type of the keto diet, you’ll be able to consume carbs when you’re working out.
- The high-protein ketogenic diet. This form of keto usually contains 60% fat, 35% protein and 5% carbs.
A nutritionally balanced diet is more than “healthy fat” and “healthy meat”
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Most people following a keto diet will eat low-carb foods with high levels of protein and fat, including plenty of eggs, fatty fish, full-fat cheese, and red meat, while completely eliminating or strictly limiting foods that are higher in carbs such as whole grains, legumes, fruit and some vegetables.
“A diet that heavily restricts or eliminates entire food groups, like a strict keto diet, isn’t ideal for your body long term,” Rodriquez says. “Fruit and vegetables are carbs — and you need them!”
Recent research agrees. In fact, in a 2018 study of almost half a million Europeans, research showed that diets with a “lower nutritional quality” (too little vegetables, fruits, legumes, etc.) were associated with higher risks of certain types of cancer.7
You don’t have to give up the foods you love to reach your weight loss goals, Rodriquez explains. “A meal plan that emphasizes non-starchy vegetables, a moderate amount of lean protein, and a balanced amount of fresh fruit, whole grains and healthy fats can help you feel your best and may help you lose weight.”
It might not be as easy as it sounds
Like many fad diets, the keto diet is hailed as a quick way to lose weight. But as Rodriquez cautions, some of this initial weight loss might not be the real fat burn you’re anticipating — there’s a chance you’re just dropping water weight as your body starts to use other processes to function. And even worse, you could be losing muscle mass.
The keto diet may be difficult to maintain after weight loss because it encourages the body to burn energy through stored glucose, and it puts the body into a state of starvation. And this doesn’t mean the physical feeling of hunger: when the body is starved of sugars, it wants to start breaking protein down into carbohydrates for fuel.8 This may happen shortly after eating more than the minimum amount of protein needed for ketosis, which means you need to eat just the right amount to prompt your body to burn fat instead of protein and carbohydrates.8 Without the careful guidance from a doctor, dietitian, or nutritionist, you may struggle to maintain ketosis. (If you’ve ever wondered why you’re gaining weight on a diet, there could be a number of reasons.)
What’s more, it’s extremely easy to eat too many carbs and throw your body out of ketosis. To put it into perspective, most keto diets aim for under 50 grams of carbohydrates per day — the amount of carbs in almost one can of cola. Eat more than this, and your body will use the carbohydrates for energy — and effectively stop your body from using its other energy stores.
So … is keto healthy and is it safe for weight loss?
That really depends on your health and medical history, Rodriquez says. Keto is still being studied as a weight loss option and doesn’t work for everyone.
Recent studies of the ketogenic diet haven’t necessarily proven it to be more effective than other diets. In a small study, overweight and obese men were placed on two different diets with the same total calories. First, they followed a high-carb, lower fat diet for four weeks. Next, they followed a lower carb, higher fat keto diet for four weeks. Researchers found that the keto diet did not result in increased body fat loss, and that much of the weight loss during the keto diet may have been water weight.9
In a separate study, adults who ate low-carb diets that focused on animal protein and fat sources had a higher risk of mortality than those who got their protein and fat from vegetables, nuts and whole grain breads.10
Weight loss should be about balance, not restriction
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You can support your weight loss by enjoying a nutritionally-balanced menu that taps into important food groups without derailing your progress.
The keto diet has the potential to be very high-calorie, given its emphasis on protein and fat. If weight loss is your goal, you will still need to create a calorie deficit: eating fewer calories than your body uses each day, Rodriquez says.
“Depending on your needs, following a 1200-1500 calorie meal plan (sometimes more) that includes a balance of nutritionally-dense foods can support your weight loss efforts,” she explains.
Rather than filling your plate with too much fat and protein, Rodriquez suggests including these items in your meals.
1. Eat plenty of non-starchy vegetables, like spinach, broccoli, and bell peppers.
2. Eat a moderate amount of:
- Lean protein (grilled chicken, eggs, fish)
- Fats (like olive oil, avocado, nuts, nut butter and seeds)
These will help you feel full and satisfied throughout the day. She also recommends enjoying a hearty, protein-rich breakfast in the morning.
3. Enjoy smaller amounts of:
- Dairy products
- Fresh fruit
These items will add more variety to your meals, but Rodriquez suggests enjoying smaller servings. “The bulk of your meals should come from non-starchy vegetables, lean proteins, and healthy fats.” she says. (Here’s how to get the perfect portion every time.)
“Balance is key,” Rodriquez says. “Don’t let a strict diet or food fad keep you from reaching your weight loss goals in a healthy way.”
Stephanie Eng-Aponte is a copywriter for Jenny Craig, based in Carlsbad, CA. Stephanie has focused on writing within the health and wellness space for the last several years, but has dabbled in the tech and environmental industries. Stephanie employs a “eat first, write later” approach to food blogging and enjoys the occasional Oxford comma. Outside of writing, you can find them photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.
Favorite healthy snack: Green apple slices with sunflower butter
Briana is a Registered Dietitian Nutritionist and Certified Personal Trainer for Jenny Craig, based in Carlsbad, California. She is passionate about utilizing food as functional and preventative medicine. Guided by a simplistic and optimistic approach, Briana’s philosophy is to help people improve their health and achieve their goals through the development of sustainable habits to live a healthy life. In her free time, you can find her strength training, indoor cycling, coffee tasting, and at local eateries with her husband and two dogs.
Favorite healthy snack: peanut butter with celery alongside a grapefruit-flavored sparkling water (so refreshing!)
This article is based on scientific research and/or other scientific articles and is written by experienced health and lifestyle contributors and fact-checked by Briana Rodriquez, RDN, Registered Dietitian Nutritionist at Jenny Craig.
Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.
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Edited by Stephanie E - Jenny Craig