This is called the metabolic switch, and research suggests that alternating between using glucose and ketones for energy — or eating and fasting — could be beneficial. Technically speaking, eating or drinking any calories breaks a fast.
Because the broadest definition of "fasting" is to refrain from food, technically speaking, any food will break a fast. Foods include: Grains, such as breads, cereals, oats, bagels, pasta, rice, quinoa, tortillas.
Food and drinks that contain calories
Strictly speaking, any amount of calories will break a fast. If a person follows a strict fasting schedule, they should avoid any food or drinks containing calories. Those following a modified fasting diet can often eat up to 25% of their daily calorie needs while fasting.
There are certain foods that aren't good to consume as part of an intermittent fasting regimen. You should stay away from foods that are calorie-dense and contain high amounts of sugar, fat and salt. “They won't fill you up after a fast, and can even make you hungrier,” Maciel says.
In short, no, diet sodas that are truly calorie free will not disrupt your fasting state.
You may need a longer or shorter eating window, or you may want to try out a new protocol entirely. Decrease (or increase) your calorie intake within your fasting window. Aim for 7–9 hours of sleep. Cut back on processed foods.
The easiest way to follow the 12-hour fast is to include the period of sleep in the fasting window. For example, a person could choose to fast between 7 p.m. and 7 a.m. They would need to finish their evening meal before 7 p.m. and wait until 7 a.m. to eat breakfast but would be asleep for much of the time in between.
Potential Drawbacks of Intermittent Fasting
If you're not already used to skipping meals or not eating for an extended period of time, the hunger and fatigue that can occur when starting IF can be difficult to handle. Other side effects can include insomnia, irritability, headaches, and nausea.
Don't rush into extreme fasting: Jumping into extended fasts like 24-hour or 48-hour windows without proper preparation can be counterproductive. Start with shorter fasting periods (12-16 hours) and gradually increase the duration as your body adapts.
Yes, You Can Consume Some Vitamins When Fasting
Some supplements, including water soluble vitamins, collagen, electrolytes and probiotics won't break your fast. However, any food that contains calories — such as gummy vitamins, bone broth or protein powder — will break your fast.
After fasting, it is important to prioritize foods that rich in fiber, such as fresh fruit and vegetables, whole grains, and lean proteins, such as white fish and chicken. These help to manage hunger pangs and maintain muscle mass.
For those aiming to lose belly fat, the 16/8 method is often recommended as the best intermittent fasting window to lose belly fat. By fasting for 16 hours and eating within an 8-hour window, you give your body enough time to burn stored fat while still allowing for a manageable eating period.
An easy way to achieve this is to push dinner a little earlier or skip the late-night snacks. Healthy individuals may consider going longer (13 to 16 hours) to reap even greater benefits in terms of fat-burning.
Eat a normal, healthy diet one day and then completely fast or have one small meal the next day. Usually, the small meal is fewer than 500 calories. Eat a normal diet five days a week and fast two days per week. Eat normally but only within an eight-hour window each day.
Chewing gum with sugar can break your fast, especially if you chew multiples of it. Sugar-free gum has no sugar, so you can chew it while fasting. Gum may help control hunger while fasting and freshen your breath.
One of the most common questions is whether apple cider vinegar (ACV) will interrupt your fasting state. The short answer is a comforting no. ACV is low in calories and doesn't contain a significant amount of carbohydrates, which means it won't cause an insulin spike that could potentially disrupt your fast.