The keto diet varies in terms of definition, but it’s essentially an eating plan that is low enough in carbohydrates that people start using fat for fuel and energy as opposed to carbohydrates.
When people are eating low enough in carbohydrates, they can enter the state of ketosis. Even if they’re not eating, they can enter the state of nutritional ketosis. Ketosis happens when the body relies on the breakdown of fat and the byproducts of this, which is ketones, for energy, as opposed to using carbohydrates for fuel.
There are a lot of ways to tell. There are mechanisms out there that can test your breath, that can check your blood, that can even check your urine. But most people are able to tell. A lot of times, they might feel thirstier. They might be urinating more frequently, even lose a few pounds pretty quickly in the first few days. It can also cause a change in tastes, like a metallic taste in the mouth or a change in your breath. It can affect your stomach sometimes, causing a little bit of nausea, decrease in appetite or energy, sometimes difficulty sleeping, especially in the beginning.
Intermittent fasting comes in a variety of different forms: the most common being time-restricted feeding, where most people will eat for an eight-hour period of time during the day, and then fast for 16 hours until the next day and continue that cycle.
During periods of fasting, especially when we’re not eating anything and we’re not eating carbohydrates, our body really has to turn to an alternative fuel source, which is fat. So it breaks down fat, which can lead to more ketones as a source of fuel and energy since we’re not really eating and don’t have that immediate source of carbohydrate.
That can vary depending on which keto plan somebody is following. But essentially, animal protein is very low in carbohydrates. Most fat sources are also low in carbohydrates. So, we're talking about things such as beef, chicken, fish, eggs; certain oils, mayonnaise, certain types of cheese and vegetables.
Some keto plans permit other foods, such as nuts and fruit, but it really depends on how strict of a low-carb plan somebody is following.
Avoid anything that is really high in carbohydrates, such as simple sugars, processed sugars, juice, starches, breads, potatoes, corn, rice. Even fruits can be very high in carbohydrates and sugar, depending on the fruit type, which is why a lot of people limit those as well.
Fruits that are higher in sugar include tropical fruits, such as pineapple, grapes, bananas, mangoes, papaya. Fruits that are lower in carbohydrates include berries, such as blueberries, raspberries and strawberries.
Any time somebody does a diet, it really should be an eating plan that is a permanent solution because any time someone does a temporary change in eating and then goes back to eating the way they were beforehand, they run the risk of regaining the weight that they had lost.
In general, I only recommend people follow any type of eating plan, whether it’s keto, paleo, or otherwise, if they’re really committed to it pretty much forever.
A good candidate for a keto eating plan is somebody who is very motivated, enjoys the food in the plan, and wants to do it forever because really, it’s a long-term solution and not a short-term plan.
The people I usually recommend not to do it are people who for example cannot eat protein because they have advanced kidney problems. Women who are pregnant or who are nursing really should not be in the state of ketosis. It potentially has some effects on the developing fetus or on nursing of the child. Anyone with a history of eating disorders: binge-eating disorder, anorexia. Cutting out carbohydrates can worsen the cycle and make eating disorders worse in the long run.
This was a very popular diet a few years back, but a lot of people still are following it as an eating plan. Essentially, it’s sort of going back to the basics as we would imagine our ancestors would have eaten, especially whole foods, unprocessed foods, but avoiding certain foods, especially dairy and grains. The diet really focuses on protein and especially lean proteins, such as fish, chicken, eggs, nuts, fruits and vegetables, including root vegetables such as cassava.
Meat consumption on a paleo plan is considered acceptable, but generally, leaner cuts of meat are preferred. I usually recommend grass-fed meats as opposed to grain-fed meats. It really depends on your level of carbohydrates because if you’re eating foods that are higher in carbohydrates, such as fruits, carrots, more starchy type vegetables. You really don’t want to be eating very high-fat foods as well because the conjunction of high-fat and high-carbohydrate foods together can be problemsome.
A good candidate for a paleo plan is somebody who enjoys the foods in the plan, wants to continue it indefinitely or for at least the majority of the time. Like I said, anything that’s considered temporary then leads back to old eating habits will usually result in weight regain.
The health benefits of eating foods that are whole, natural, high in vegetables, low in sugar are numerous.
One, it can help promote weight loss. In my clinic, I have a sample of a five-pound fat mass that I sometimes show patients who feel like five pounds isn’t a lot of weight loss. But it really is a lot. A visual demonstration can be helpful.
Weight loss is a benefit of both keto plans and paleo plans. Any diet that’s limiting calories and is easy to stick to can help people lose weight. When people lose weight, their general health and well being improve. They lower their risk of cancer, high blood pressure, heart disease, diabetes, depression, sleep apnea and dementia. It goes on and on.
I haven’t yet seen that many people are following it. It seems to be essentially a paleo-type plan with a focus on plant-based foods. About 75% of daily food intake is coming from fruits and vegetables and only a small amount is coming from meat. It is more of a plant-based paleo, where you are still eliminating beans and starches, sugar, dairy foods and grain products, such as wheat.
The benefits are similar to a paleo or a keto-type plan when it comes to weight loss, but there is evidence that focusing on more plant-based foods might also help in terms of cardiovascular risks.
There is a lot of debate out there, but I don’t think anyone can argue that eating a lot of vegetables and whole foods and avoiding processed refined foods isn’t good for your health.
Any type of eating plan really depends on your personal preferences, what you enjoy eating, what you think you could continue in the long run because it shouldn’t be a temporary fix.
The data has shown that short-term diets usually fail in the long-term because people will regress to their prior eating habits. So definitely think about something that’s simple, that is safe, but most importantly, sustainable for you or that can be continued indefinitely.
Lightly edited for clarity
Watch the San Diego Health video with Susan Taylor and Dr. Harris discussing the difference between the paleo diet and the intermittent diet.