Intermittent Fasting 101

What is intermittent fasting?

Intermittent fasting is best defined as a way of eating that involves extended periods of not consuming foods when a person normally would. This could consist of alternating days of normal eating with days of fasting, where you only consume water and no calories. The fasting phase could also occur during a given day, such as only eating during certain times or a specific number of hours each day.

Side Effects

Intermittent fasting very likely means you will not be getting the daily five-to-six servings of grain foods, the five or more servings of fruits and vegetables, or the daily requirements for key nutrients, such as fiber. With this in mind: 

You may feel tired and/or lack energy all the time.

Carbohydrates provide natural energy to our bodies. The common problem with consuming carbs is that people tend to overindulge in the wrong ones. The key factor is finding the appropriate amount of carbs that your body needs as well as making sure you are consuming carbs from a variety of sources, not just one. Carbohydrates are mainly found in fruits, starchy vegetables, grains (rice, breads, pasta, cereals, tortillas), and dairy products such as milk and yogurt. Including a variety of these food groups will provide the energy your body needs to sustain your activities. 

You may be far more likely to experience nutrient deficiencies.

Daily servings of food groups are encouraged for a reason, which is to provide your body with the nutrients it needs each day to remain healthy and sustainable. Carbs, specifically foods made with enriched grains such as breads, cereals, and tortillas provide key nutrients such as: 

  • Fiber – a nutrient that supports a healthy heart by reducing blood cholesterol. It also promotes a healthy digestive system. Whole grains are among the best sources of fiber, since fiber is concentrated in the grain’s bran and germ. 
  • Folate – a B vitamin most associated with preventing neural tube defects during early pregnancy. By the time most women are aware of being pregnant, the critical window for folate has already passed. That’s why it’s so important to get adequate folate before a woman becomes pregnant. Folate is also important for heart health.  
  • Thiamin – also known as vitamin B1, it’s important for cellular function and energy metabolism. 
  • Niacin – also called vitamin B3, is another B-vitamin with an important role in metabolism. It also supports a healthy digestive system, skin, and nerves. 
  • Iron – a mineral the helps bring critical oxygen to cells throughout the body. About half of a person’s daily iron intake comes from grain foods. 
  • Zinc – a mineral that aids the immune system in protecting the body from bacteria and viruses. It’s also important during pregnancy and early childhood for human development. 
  • Magnesium – a nutrient with many roles in the body, including bone health, muscle and nerve function, and blood pressure regulation. 
  • Calcium – a mineral most associated with bone health, but it has other benefits as well including supporting cardiovascular health. 

You may feel hungry between meals, or all the time!

Grain foods help us feel full between meals, so if you are practicing intermittent fasting, where you aren’t consuming grains on a normal eating schedule, your body may feel less full than usual. One study found that oatmeal for breakfast may increase satiety and lead to a lower-calorie lunch, showing that regularly consuming grains, along with other recommended food groups, will satisfy your body’s need for food when compared to intermittent fasting.

You may begin hating the lack of variety in your diet. 

Including foods from all food groups (or a minimum of three) in each meal helps to provide sufficient nutrients for your everyday activities – that means lots of colorful fruits and vegetables, both whole grain and enriched grain products, and plenty of low-fat meat and dairy. Variety is the spice of life – and diet – so it’s easy to imagine how boring, not to mention unhealthy, your diet can become if you avoid as many carbs as possible. 

You may lack – and miss out on the benefits of – an especially important nutrient – dietary fiber. 

Fiber is especially important in the diet, as under 4 percent of the US population meet the fiber requirement. Fiber is critical to a healthy microbiome and is associated in numerous meta-analyses with reduced risk of nearly all chronic diseases. This includes various cancers, coronary heart disease, and diabetes. These meta-analyses have been conducted with a variety of countries with various baseline diets. They show that those who eat the most dietary fiber, have a lower risk of type 2 diabetes. For patients with diabetes, fiber is important for slowing the rise of blood sugar and other aspects of the disease. Higher fiber intakes are also associated with reduced risk of all-cause mortality. In the obesity fight, foods high in fiber improve satiety, which may help in averting obesity and helping dieters stick to their healthy eating habits. 

You may experience digestive distress. 

You need insoluble fibers, which help with digestive functioning and feelings of fullness. Soluble fibers can also impart satiety and do things like trap glucose and cholesterol to slow or inhibit their digestion and absorption. Most fibers are fermentable, but soluble fibers ferment rapidly in the upper colon while insoluble ones add bulking and help move things through the colon. The fermentation in various parts of the colon is critical to feed the colonic microbiome and for producing the short-chain fatty acids which help keep cells lining the colon healthy and improve other functions. 

The above information was contributed by Glen Gaesser, PhD, Sylvia Melendez-Klinger, RD, and Julie Miller Jones, PhD, LN, CNS.