Fast foods: what to eat when intermittent fasting for weight loss

Fasting is defined as the intentional restriction of calorie intake over a limited period of time and has numerous health benefits including weight loss, protection against disease and improved longevity. While the period of limited calorie intake known as the ‘fasting’ hours is evidently an integral part of fasting, what you eat during ‘feasting’ hours is also important. So which foods should you prioritise and which should you avoid to boost the benefits of your fast when you can eat?

What is intermittent fasting?

Fasting is the ancient practice of food restriction that promotes weight loss by metabolising the body’s fat reserves instead of relying on readily available blood glucose from food. Intermittent fasting is used for weight loss and can easily be incorporated into everyday life, as it follows the body’s natural circadian rhythm that controls metabolism. One popular method of intermittent fasting is the 16:8, which alternates between feasting for eight hours during the day before fasting for 16 hours overnight. Fasting intentionally limits the body of nutrients, triggering a ‘metabolic switch’ as the body shifts from using energy from blood glucose in food to ketones metabolised from its own fat reserves, known as the G-K switch. 12 to 16 hours into a fast, blood glucose levels drop and the body begins to metabolise fat through the process of ketosis, producing ketones that are oxidised by the brain for food and promoting weight loss [1]. As the body is placed under increasing nutrient stress, the process of autophagy begins, during which cells reuse damaged organelles to rejuvenate. Weight loss associated with fasting reduces the risk of obesity-related diseases, such as diabetes, sleep apnoea and certain cancers [2]. While cellular renewal triggered by autophagy plays a key role in preventing age-related diseases including cancer, cardiovascular disease and metabolic disease [3].

The post-fast period or ‘refeeding’ stage is emerging in research as an important part of fasting that can boost cellular and tissue regeneration.

The best foods to eat post-fast

The post-fast period or ‘refeeding’ stage is emerging in research as an important part of fasting that can boost cellular and tissue regeneration [1]. During your long-awaited feast hours, it is important to replenish your energy with the right balance of macronutrients from the triumvirate of carbohydrates, protein and fat. Eating the right foods post-fast optimises your fast and can prolong its weight loss and health benefits. It is easier to make healthy dietary choices when you have planned ahead, so prepare recipes, meal plans and shopping lists before the feasting hours to avoid the temptation of breaking your fast with the first, most convenient food you can find. Carbohydrates contain natural energy from sugars, starches and fibre that you can get from eating fruits, vegetables, whole grains and lentils. Including plenty of vegetables and fruit in you meals is important as they are both high in nutrients and help your body feel fuller for longer using less calories.
Healthy options include sandwiches made using wholegrain bread with a side salad at lunch, and a side plate of roasted vegetables served alongside dinner [4]. Proteins found in salmon, seafood, eggs and chicken help build and maintain muscle so are also good options [5]. During fasting, the body metabolises existing fat supplies without touching the protein found in muscle, so it is possible to weight train while fasting without preventing muscle growth [6]. Lastly, monounsaturated and polyunsaturated fats from milk, ghee cheese, nuts and seeds provide nourishment and are essential to a post-fast diet. Micronutrients from berries, cruciferous vegetables and smoothies are also integral post-fast to prevent deficiencies and can be eaten alongside dietary supplements for additional benefits [5].

Foods to avoid post-fast include the usual suspects of processed meats, trans fats and refined sugar and starches that you should limit in your everyday diet anyway.

Foods to avoid post-fast

Eating unhealthy foods once you finally break your fast can counteract the benefits of fasting. Foods to avoid post-fast include the usual suspects of processed meats, trans fats and refined sugar and starches that you should limit in your everyday diet anyway. These food types contain minimal nutrients and do little for fullness so should be avoided especially as your body readapts to eating during feasting hours. Sugar and refined carbohydrates are especially detrimental as they can cause a rapid release of blood glucose after the body has depleted its own glucose supplies during fasting. Drinks like flavoured coffee, alcohol and fruit juice drinks are a pernicious source of unnecessary sugar and calories. Alternatively, try black coffee without the usual embellishments of sugar and cream, or still or carbonated water [5]. Post-fast, your body may be sensitive to high-lactose dairy and raw high-fibre vegetables like broccoli, cauliflower and brussels sprouts, as they can cause bloating so try to limit your intake initially especially following a prolonged fast [7].

Overeating while fasting

It is also important to avoid over-congratulating yourself by indulging in excessive eating when you finally reach your feast day. Despite the ‘refeeding’ stage of fasting being known as the feast hours, try to avoid overeating when you do eat, as this can increase postprandial lethargy and reduce energy. While occasionally overeating is offset by the body’s metabolism, constant overeating can lead to high blood pressure, diabetes and obesity that impair the body’s ability to maintain the metabolism [8]. Overeating high-fat food for just 24 hours can have an immediate impact on the metabolism and can impair glucose control. Therefore, it is important to resist indulging in high-calorie, high-fat food post-fast and instead eat them in moderation throughout the week or on one designated ‘cheat day’. Another way to counteract the effects of overeating if you find it impossible to avoid is by exercising before or after consuming a large meal, as this reduces postprandial blood glucose levels and increases the body’s sensitivity to insulin, avoiding energy crashes later [9]. Fasting is a dietary change that requires commitment during both fasting and feasting hours, however its tangible benefits to weight loss, health and longevity make fasting worthwhile.