Fasting – virtually unheard of as a diet strategy a few years back – is now mainstream with individuals regularly committing to fasting regimes which may see them slash their calories a couple of times each week, or limit their eating to a set number of hours each day.
As fasting is a relatively new strategy to support weight loss, the research that helps to understand the various mechanisms by which it works is still in progress. As such, we do not necessarily have all the answers when it comes to fasting, and the ‘rules’ stated tend to be anecdotal.
This is definitely the case when it comes to the question of ‘what actually breaks a fast?’ with a range of varying opinions and fasting rules dominating online information sources.
So, what does the science say about the foods and drinks that will break your fast if you are trying to maximise your weight loss results?
Technically, consuming any food or drink that contains a significant amount of calories will break the fast. This includes coffee with milk, protein shakes, bulletproof coffee or a piece of fruit. While these foods are relatively low in calories, they still offer 50-100 calories per serve, which will have an impact on the hormones that influence glucose levels, thus ceasing the beneficial metabolic processes that justify fasting.
This then begs the question of ‘what is a significant number of calories?’
The true answer to this we do not know, but there is one frequently mentioned study that is said to have examined the impact of including BCAA’s (Branch Chain Amino Acids) in a morning fast, which equated to 50 calories – and it was found that there was no significant effect on weight loss.
While the source of this information or study is unknown, this is largely where the rationale comes for an insignificant number of calories equated to 50 or less.
In food terms, this would also suggest that tea or coffee enjoyed with a dash of milk, a few berries, or some plain vegetables such as cucumber or carrots, will disturb the metabolic processes that give fasting its benefits, especially if it fends off hunger.
What about zero calorie sweetened foods?
This would then suggest that foods that have zero calories, as is the case with diet products that use artificial or natural sweeteners to achieve sweet tasting foods (minus a significant number of calories), can be consumed freely during the fasting period. However, while this may sound reasonable, there is some evidence to show that artificially sweetened foods in particular can result in a release of insulin, the hormone that controls fast metabolism and drives hunger.
This means that while the drink or jelly may not technically contain calories, it may still disrupt the fast and directly impact your appetite – and as such is best avoided.
Fasting means fasting. The fewer calories you are able to consume during fasting, the better your results are likely to be. If you absolutely cannot start the day without a coffee, then yes, you will likely get away with a long black and a dash of milk. But forget the latte because that, along with any other real food, will negate the beneficial affects you are trying to achieve via fasting.
Susie Burrell is a nutritionist. Continue the conversation on Twitter @SusieBDiet.