Keto Fasting: Sustaining A Long-Term High-Fat Diet

The ketogenic diet, or keto, is a popular diet strategy that involves cutting carbs and fueling the body with fat. While keto can lead to quick weight loss in the short term, critics argue that much of this is water weight and that long-term research on the diet is lacking.

Intermittent fasting (IF) is another popular diet approach that restricts when or how much you eat, rather than what you eat. IF can be done in several ways, such as the 5:2 diet, where five days are normal eating days and two are extremely low-calorie fast days, or time-restricted eating, such as eating for 8 hours and fasting for 16.

Combining keto and IF has become a trendy approach for those looking to take their weight loss to the next level. This strategy makes sense as both methods increase ketone levels in the body, which may help accelerate weight loss. However, there is a lack of rigorous research on the combined approach, and it may not be suitable for everyone.

Before starting any new diet, it is important to consult a healthcare professional to ensure it is safe and appropriate for your individual needs.

Fasting for short periods

Intermittent fasting (IF) is a popular dieting trend that can be done in conjunction with the keto diet. It involves an intentional approach to eating that cycles between periods of eating and fasting. It is not a diet in itself but influences when you eat.

There are different ways to practice IF:

• Time-restricted eating: Eating only during an 8-hour window in a day, for example, from 9 am to 5 pm, and fasting for the remaining 16 hours.
• Alternate-day fasting: Choosing two or more days a week where you restrict your calorie intake to 400-600 calories.
• Whole-day fasting: Eating normally for five days and then restricting calories to 500-600 for two non-consecutive days.
• 16:8 method: Fasting for 16 hours and eating during an 8-hour window.
• OMAD (One Meal a Day): Fasting for 23 hours and eating during a 1-hour window.

IF can be challenging for beginners, so it is recommended to start with a smaller fasting window, such as 12 hours, and gradually increase it. It is also important to stay hydrated by drinking water, plain tea, or black coffee during the fasting period.

• Decide on the length of your fast and start with a smaller window if you are a beginner.
• Avoid eating during the fasting window, but you can drink zero-calorie beverages.
• Stay hydrated and add electrolytes if you are fasting for longer periods.
• Exercise during your fasting window but consider doing intense workouts closer to your eating window.
• Plan your meals ahead of time to avoid making last-minute food choices when hungry.
• When your fasting window ends, break your fast with balanced and nutrient-dense foods.

Intermittent fasting offers several health benefits, including:

• Reducing insulin and blood sugar levels.
• Improving cardiovascular health by lowering cholesterol and blood pressure.
• Triggering autophagy, a cleanup process in the body that protects against oxidative stress and keeps cells younger.
• Reducing the risk of diseases by lowering inflammation and potentially helping to kill cancer cells.
• Improving mental clarity by boosting brain-derived neurotrophic factor (BDNF), which is linked to better learning and mood.

While IF has many potential benefits, it is not suitable for everyone. It is important to consult a healthcare professional before starting IF, especially if you have any medical conditions, are pregnant or breastfeeding, or have a history of disordered eating.

Increasing physical activity

While on a keto diet, it is important to understand how your body works when you exercise. The body is an adaptable machine that can handle a variety of situations and stresses, from sitting on the sofa to (with training) climbing Mount Everest. To perform efficiently in all scenarios, the body uses a number of 'metabolic pathways' to provide energy, generally utilizing the best one for the job.

Metabolic Pathways

Ketosis

Ketosis is the process by which fats within the body are oxidised and broken down into a series of compounds including ketones, which are then used for energy. This is one part of the 'aerobic' metabolic pathway (which requires oxygen).

A person is generally considered to be in ketosis when ketones are the primary fuel source being used over other sources. This taps into the body's huge energy reserves of fat, but it is generally not able to produce large amounts of energy at any given time. Therefore, ketosis alone is not an ideal fuel source for short periods of intense activity.

Glycolysis

This is the process that uses glucose as the primary fuel source for the body. For most people eating a Western diet, this is how you fuel your day. Glycolysis quickly makes use of glycogen stored directly in the muscles or in the liver to provide energy.

Moderately high-intensity exercise is fuelled by this process, although for very short, intense bursts of exercise under 10 seconds (e.g., 100m sprints), alternative sources are required. The body only stores a limited supply of glycogen, meaning over longer periods of exercise, such as long-distance runs, this source of energy can run out (this is why you see marathon runners eating gels and sugary snacks).

Phosphagen System/ATP-CP System

For extremely intense, short bursts of exercise like quick sprints and heavy weight lifting, neither ketosis nor glycolysis can provide the energy needed fast enough. In this case, the body uses the phosphagen system, also called the ATP-CP system. This uses creatine phosphate stored in the skeletal muscles to quickly provide energy in the form of ATP (adenosine triphosphate).

Once you limit your carb intake, your body quickly depletes its remaining glycogen stores until ketosis can supply sufficient energy to compensate. This transition often results in a point where you have run out of glycogen, but aren't producing enough energy from fat yet, which is why many people report feeling tired and exhausted in the first few days of a keto diet.

Exercising without these glycogen stores, muscles find that after the first 10 seconds or so (where they were fuelled by creatine phosphate), their energy source disappears, resulting in reduced performance. It's only after a minute or two that fat oxidation and ketosis ramp up and are able to supply enough energy for moderate-intensity exercise through ketones.

This gap in energy supply can have a detrimental effect on sports and activities that require short, intense movement, such as weightlifting, short-distance running, high-intensity interval training, and team sports like soccer and rugby.

How to Eat Keto for Exercise

Macronutrients

Getting the correct fuel for your workout is pivotal for success. As discussed, there are three main fuel sources: fat, glucose, and creatine. But another key requirement for optimal exercise is making sure we don't lose the muscle we currently have. Read on for how to adjust your macronutrients for exercise:

Protein - Muscle loss can be a real concern on any diet, so protein is usually the first macronutrient to consider when calculating ratios. You can fuel your workout with fats or carbs, but you need protein to rebuild and maintain your muscles. This is why it's critical to get enough protein into your diet if you're planning on exercising regularly.

Prevailing advice suggests that athletes or those who exercise regularly should aim to consume between 1.4 and 2g of protein per kilogram, or between 0.6 and 0.9 grams per pound of body weight. If you're doing light cardio regularly and looking to lose weight but not lose muscle, you may want to be around the 1.4g per kg mark (0.6 per pound). If you're a serious weightlifter looking to gain mass, you'll need to be at the top end of the range, or even higher for bodybuilding.

One concern with protein consumption on a keto diet is that it is possible to convert protein into glucose. This can occur if you eat large quantities of protein in a short space of time, and it's called 'gluconeogenesis'. If you are exercising regularly, this excess protein may be beneficial as it can be converted into glucose to help fuel your workouts. However, too much glucose will kick your body out of ketosis, so it is important to be mindful of your protein intake if you are trying to lose weight. Try to distribute your protein intake throughout the day to avoid spikes, while consuming a little more immediately after any workouts to reduce muscle loss.

Carbohydrates - If you are highly active, it is likely that you will be able to increase your carb intake above the general keto recommendation of 20-35g per day without significantly affecting your state of ketosis. If your activity needs high intensity, such as soccer, rugby, or short-distance running, then upping your carb intake will likely help you in these activities.

The key to increasing carb intake is to manage the timing of consumption. There are two general approaches:

Targeted Ketogenic Diet - This approach involves targeting when you eat carbs to your workout times. Try consuming 25-50g of easy-to-digest carbs immediately before working out, around 30 minutes before is ideal. This should give an energy boost for the exercise, with the glucose

Reducing carbohydrate intake

Reducing your carbohydrate intake is a key step in achieving ketosis, and there are several ways to do this without feeling overly restricted. Here are some detailed tips to help you cut down on carbs:

Limit Refined Bread and Grains

Gradually reduce your consumption of refined grains and bread products. Start by eliminating packaged snacks like crackers and biscuits, then move on to baked goods like cookies and muffins. Eventually, cut out bread and other refined grain products altogether.

Find Alternatives with Vegetables

Instead of relying on refined grains, opt for low-carb vegetable alternatives. For example, use shredded zucchini or yellow squash instead of pasta, mashed cauliflower instead of mashed potatoes, and cauliflower crust for pizza.

Explore Alternatives to Flour

When baking or cooking, substitute low-carb flours like almond or coconut flour for traditional white flour. These alternatives are more flexible than you might think and can be used for everything from fried chicken to muffins.

Curb Your Intake of Sugar-Sweetened Drinks

Sugar-sweetened drinks, including sodas and sweetened iced teas, can add a significant amount of carbohydrates to your diet. Opt for flavored seltzers or plain water instead. If you're craving something more flavorful, infuse your water with berries or herbs like mint for a natural sweetness.

Cut Back on Refined Grain Bread

While whole grain bread is a healthier option, even these can be consumed in moderation. Refined grain bread, such as white bread, is often high in carbs and can cause blood sugar spikes. If you can't give up bread completely, try an open-faced sandwich to reduce your carb intake by half.

Choose Lower-Carb Snacks

Snack foods like chips, pretzels, and crackers are usually high in carbs and low in protein and fiber, leaving you unsatisfied and prone to overeating. Opt for snacks like nuts, cheese, and eggs, which are lower in carbs and higher in protein and healthy fats.

Start Your Day with a Low-Carb Breakfast

Breakfast cereals and granola can be loaded with hidden carbs and sugar. Instead, start your day with eggs or other low-carb options like yogurt, crustless quiche, or nut butter on celery sticks.

Use Sugar Alternatives

If you enjoy sweetening your coffee or tea, try using sugar alternatives like stevia, erythritol, or xylitol. These options can help you satisfy your sweet tooth without adding extra carbs to your diet.

Be Mindful of Restaurant Meals

When dining out, be mindful of the carb content of your meal. Starch sides like potatoes, rice, or bread can add a significant number of grams of carbs to your meal. Consider ordering extra vegetables or a side salad instead to increase your fiber intake and curb your carb consumption.

Focus on High-Protein Foods

Increasing your intake of high-protein foods can help you feel fuller for longer, reducing cravings and boosting your metabolic rate. Examples of high-protein foods include lean meats, fish, eggs, and dairy products.

Remember, reducing carbohydrate intake is just one aspect of achieving ketosis. Combining it with other strategies like intermittent fasting and increasing physical activity will help you reach and maintain ketosis more effectively.

Increasing healthy fat intake

When following a keto diet, it is important to remember that not all fats are created equal. While the keto diet is high in fat, it is essential to focus on healthy fats from nutrient-dense, whole foods. Here are some tips and food choices to help you increase your healthy fat intake while on a keto diet:

Understanding Different Types of Fats

There are three main types of fats to be aware of: saturated fats, monounsaturated fats, and polyunsaturated fats. Saturated fats, such as those found in coconut products, dairy, and red meats, were once believed to be harmful. However, recent research suggests that saturated fat may not be as detrimental to heart health when consumed in moderation. Monounsaturated fats, found in avocados and olive oil, are known for their health benefits, including improving blood vessel function and blood sugar control. Polyunsaturated fats include omega-3 and omega-6 fatty acids, which are essential for brain and heart health. Fatty fish like salmon and tuna are excellent sources of polyunsaturated fats.

Best Sources of Healthy Fats on Keto

• Fatty Fish: Aim for salmon, tuna, mackerel, sardines, and anchovies, which are rich in omega-3 fatty acids and protein.
• Avocados and Avocado Oil: Avocados are versatile and packed with heart-healthy monounsaturated fats, fiber, and essential vitamins and minerals. Use them in salads, dips, or smoothies, or enjoy them plain with a sprinkle of sea salt.
• Plant-Based Oils: Opt for olive oil, avocado oil, and walnut oil to increase your healthy fat intake. These oils are perfect for roasting or sautéing vegetables or making salad dressings.
• Nuts and Seeds: Include a variety of nuts and seeds in your diet, such as almonds, pistachios, walnuts, pecans, and pumpkin or sunflower seeds. They are excellent sources of mono- and polyunsaturated fats, plant-based protein, and fiber. Enjoy them as a snack, or add them to smoothies or salads.
• Full-Fat Dairy: Choose full-fat dairy options like heavy cream, full-fat yogurt, and whole milk. Just be mindful of the carb content from lactose.
• Coconuts and Coconut Oil: Coconuts and coconut oil provide a natural source of medium-chain triglycerides (MCTs), which are easily absorbed and used by the body. They can aid in weight loss and make it easier to transition into ketosis.
• Olives and Olive Oil: Olives are loaded with heart-healthy fats and antioxidants. Enjoy them as a snack or add them to salads or antipasti. Drizzle olive oil on grilled or roasted vegetables for a boost of healthy fat.
• Eggs: Eat the whole egg to get the full benefit of its nutrients, including healthy fats, protein, and antioxidants. Enjoy eggs in any style, add them to salads or soups, or eat them as a quick snack.
• Cheese: With hundreds of varieties to choose from, cheese is a great way to add healthy fats to your keto diet. Opt for full-fat, minimally processed options like Brie, Parmesan, feta, or Gruyère.

Creative Ways to Increase Fat Intake

• Fat-Spiked Drinks: Add a tablespoon of healthy fat to your coffee, tea, or smoothie. Try grass-fed butter, heavy cream, coconut cream, avocado oil, or MCT oil.
• Fat-ify Your Veggies: Roast, steam, or sauté your vegetables with grass-fed butter or extra-virgin olive oil. You can also experiment with flavored oils for added dimension.
• Use Avocado Everywhere: Avocados are incredibly versatile. Mash them in the shell with cilantro, lime juice, and salt for a quick guacamole, or add them to smoothies, salads, or dips.
• Stock Up on Nuts and Seeds: Keep a variety of nuts and seeds on hand for snacking or adding to smoothies or salads.
• Add Sour Cream: Opt for full-fat sour cream and use it as a dip for roasted veggies or fresh berries, or stir it into soups or smoothies.
• Choose Full-Fat Cheese: Avoid low-fat cheeses, which often have added sugar and sodium. Go for full-fat, minimally processed options like Brie, Parmesan, or feta.
• Make Homemade Mayonnaise: Mayonnaise can be added to salad dressings or used as a dip for vegetables.
• Try Tahini: This Middle Eastern paste made from sesame seeds can be added to smoothies, salad dressings, or keto bombs.
• Make Coconut Fairy Dust: Combine unsweetened coconut flakes, almonds or macadamia nuts, sunflower seeds, sesame seeds, chia seeds, and lime zest in a food processor. Sprinkle this mixture on grilled meat or veggies for an extra boost of healthy fat.

Remember, while increasing your healthy fat intake is crucial on a keto diet, it's also important to monitor your protein and carbohydrate intake to maintain ketosis.

Testing ketone levels

There are three types of ketones: acetone, acetoacetate, and beta-hydroxybutyrate. These can be measured in your breath, urine, and blood, respectively. Testing can be done through breath analysis, urine strips, or blood tests.

Breath Analysis

Breath testing is a newer method of measuring ketone levels. It measures acetone, the least abundant ketone, which is exhaled through the breath. The more acetone in the breath, the deeper the state of ketosis. Breath testing is a convenient and non-invasive method.

Urine Strips

Urine strips are a simple, affordable, and convenient way to test for ketones. They can be purchased at a local pharmacy or online. To use, dip the test strip into a container with a fresh urine sample and wait for about 40 seconds. The colour of the strip will indicate the level of ketones, ranging from light to dark, with corresponding mmol/L ketone levels.

Blood Tests

Blood testing is the most accurate way to measure ketone levels as it directly checks beta-hydroxybutyrate, the most abundant ketone. To test, wash and dry your hands, then prick your finger with a lancing device and place a drop of blood on the test strip. Wait about 10 seconds for the final reading.

Who Should Test Ketone Levels?

Ketone testing is often done for people with type 1 diabetes to monitor and prevent diabetic ketoacidosis (DKA), a medical emergency. For those on a keto diet, testing can provide objective data to confirm that the diet is working.

When to Test Ketone Levels

For those with diabetes, testing should be done when experiencing signs and symptoms of DKA, such as frequent urination, fruity or acetone-smelling breath, tiredness, and high blood sugar levels.

For keto dieters, testing can be done in the early morning or a few hours after dinner. Testing at the same time each day is recommended if monitoring ketone levels over a period of time.

Frequently asked questions