How to Lose Weight with Fasting

Fasting involves constraining the times you consume your meals and is a widespread approach to lose weight. In most cases, by limiting when you eat, you naturally consume less calories than you otherwise would, thus entering a caloric deficit and losing weight.


Before we dig into how to lose weight with fasting, we first have to understand the principles of losing weight.

The single, most important factor when it comes to changing your weight is calorie balance; the ratio between calories consumed and calories expended at any given time.

The amount of energy in an item of food or drink is measured in calories. Our bodies need energy to keep us alive and our organs functioning normally. When we eat and drink, we put energy into our bodies. Our bodies use up that energy through everyday movement, which includes everything from breathing to running.

To lose weight, you need to use more energy than you consume, and continue this over a period of time.

The principle of course applies to maintaining weight and gaining weight as well.

  • Maintaining weight: maintaining a stable weight requires the energy you put into your body to be the same as the energy you use through normal body functions and physical activity.
  • Gaining weight: if you’re gaining weight, it could mean you have been regularly eating and drinking more calories than you have been using. This is also known as a positive calorie balance.

A negative calorie balance will always result in weight loss. While other aspects such as dehydration and unhealthy weight loss (losing weight too fast by drastically cutting your energy sources for example) affect weight, these aren’t sustainable or healthy, you still need to meet your basic demand of micronutrients.

how to lose weight with fastingSource: Photo courtesy of CrossFit Inc.


Fasting is one good way to reduce the calories you consume.

Intermittent fasting is an eating pattern that involves regular periods of no food consumption. There are many strategies to implement intermittent fasting, the most popular methods include:

  • The 16:8 method, in which you fast for 16 hours and have an eight-hour eating window.
  • The 5:2 diet, where you eat normally for five days a week, then reduce your calorie intake to one-quarter of your daily needs for the other two days of the week.
  • The Eat Stop Eat diet, which involves identifying one or two non-consecutive days per week during which you abstain from eating, or fast, for a 24-hour period.

Studies looking into how to lose weight with fasting generally find that study subjects tend to consume less calories than they usually would, while hunger levels remain stable or decrease with intermittent fasting.

Most people will naturally eat fewer calories after skipping whole meals. While you might eat more than usual during your periods of eating, it’s unusual for people to completely compensate for the calories they’d have otherwise consumed if not fasting.

For example, imagine your usual lunch is 700cal and your dinner 1,000cal. On an intermittent fasting diet you might skip that lunch. While you might then consume 1,300cal for dinner, you’re unlikely to hit the 1,700cal you’d normally consume in one day. This will help you enter a negative calorie balance.

In addition, many people pay closer attention to what they eat when on a diet, generally making healthier food choices.

Fasting forces you to cut snacks

Tia-Clair-Toomey-Madison-Triplus-CrossFit-Games-2018Source: Photo courtesy of CrossFit Inc

Entering a fasting diet forces you to cut on snacks, which is the easiest way to consume less calories without having to make huge alterations to your lifestyle. To start with, simple changes are the most effective, as we’re more likely to stick with them.

People on an intermittent fasting diet have found that they can lose weight by following a diet that forces them to cut out on excesses.

Fasting can influence your perception of hunger

Some data suggests that fasting can affect hormones such as ghrelin (which stimulates appetite and promotes fat storage) and leptin (which helps regulate energy balance by inhibiting hunger, which in turn diminishes fat storage).

A 2016 study found that, while ghrelin levels increased during an eight-week alternate day fasting protocol, there was no increase in subjective hunger by the end of the study. Despite the metabolic changes, ghrelin sensitivity decreased and therefore no compensatory increase in hunger emerged.

With these metabolic changes you might feel fuller faster and hungry less often, or your perception of hunger might change as your sensitivity to hunger-related hormones changes. This could translate to fewer calories consumed and, as a result, weight loss.

Fasting and resistance training for weight loss

A 2016 study looking into the effects of intermittent fasting in athletes found that, when combined with resistance training, the 16/8 intermittent fasting method “could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.”

This means that fasting could not only help you reduce body fat, but can also aid in maintaining muscle mass.

The more physical activity we do, the more energy we use. While fasting can help you reduce the calories you consume, exercising will help you burn them. This can help you enter a negative calorie balance, just make sure you always eat enough to meet your basic energy demands.

crossfit feel goodSource: Photo courtesy of CrossFit Inc.


In essence, to lose weight you can either:

  1. Consume less calories (eat less)
  2. Burn additional calories (exercise more)
  3. Do a combination of the two

For most people “the best approach is to combine diet changes with increased physical activity,” the NHS recommends.

Fasting is a popular approach to weight loss as it restricts your eating times and, consequently, gets you to eat less calories. Intermittent fasting has been proven to be not only effective but also sustainable for weight loss.

Yet one approach does not fit all in the quest to achieve body weight control, and the best diet for weight loss is one that is sustainable and one you can stick to in the long run. If intermittent fasting makes it easier for you to stick to a healthy diet, it can have obvious positive effects on your long-term health and weight maintenance.

All content within this article is provided for general information only and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. Always consult a dietitian before making big changes to your diet.

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