Intermittent Fasting for Weight Loss: What You Should Know
Intermittent fasting is often presented online as a simple way to lose weight. You may see people talking about eating windows, fasting apps, 16:8 routines, or not eating after a certain time, as if it is suitable for everyone.
At Aster, we think it is important to be careful with this message.
Intermittent fasting may help some people reduce their overall calorie intake, but it is not risk-free. It can be particularly risky for people who have a history of disordered eating, binge eating, restrictive eating, body image distress, or an unhealthy relationship with food.
Aster does not officially endorse intermittent fasting as a standard weight loss approach. We do not recommend starting it without appropriate clinical guidance, especially if you are using weight management medication, living with a medical condition, or have ever struggled with eating patterns.
Weight loss should never come at the cost of your physical or mental health, which is why we offer free consultations for all our patients.
What is intermittent fasting?
Intermittent fasting is an eating pattern where you cycle between periods of eating and periods of fasting.
Common examples include:
16:8 fasting
Eating within an 8-hour window and fasting for 16 hours.
14:10 fasting
Eating within a 10-hour window and fasting for 14 hours.
5:2 fasting
Eating normally for 5 days a week and significantly reducing calorie intake on 2 days.
Alternate-day fasting
Alternating between normal eating days and fasting or very low-calorie days.
Although these methods are often described as simple, they can become psychologically difficult very quickly. For some people, fasting rules can create a cycle of restriction, guilt, overeating, shame and more restriction. Disordered eating and fasting can go hand-in-hand very easily.
That is one of the reasons we are cautious about it.
Why intermittent fasting can be risky
The problem with intermittent fasting is not only the fasting itself. The risk is the way it can affect someone’s relationship with food.
For some people, fasting can become a socially acceptable form of restriction. It may start as eating between 12 and 8, but gradually become more rigid, more extreme, or more emotionally charged.
This can look like:
feeling anxious if you eat outside your eating window
ignoring hunger because you are not allowed to eat yet
feeling guilty after eating breakfast or a snack
delaying food even when you feel dizzy, weak or unwell
using fasting to compensate for eating more the day before
bingeing during the eating window because you feel deprived
becoming preoccupied with food, calories or body weight
avoiding social meals because they do not fit the fasting schedule
These are not signs of a healthy weight loss routine. They are warning signs that a method may be becoming harmful.
Intermittent fasting and eating disorders
Intermittent fasting can be especially dangerous for people with a current or past eating disorder, or for anyone who has experienced disordered eating patterns.
This includes people who have struggled with:
binge eating
bulimia
anorexia
restrictive dieting
compulsive calorie counting
emotional eating followed by guilt
secret eating
purging behaviours
over-exercising to compensate for food
long periods of food restriction
obsessive weighing or body checking
Even if someone has never had a formal eating disorder diagnosis, intermittent fasting may still be risky if food already feels emotionally complicated.
A fasting schedule can make restriction feel justified. It can also make binge-restrict cycles worse. For example, someone may fast during the day, become extremely hungry, overeat in the evening, feel ashamed, and then fast again the next day to make up for it.
That cycle can become very damaging.
Why supervision matters
Intermittent fasting is often promoted as something people can do alone. But for many patients, especially those seeking medical weight management, it should not be treated casually.
Clinical supervision matters because a healthcare professional can help assess whether fasting is safe for you.
They may consider:
your medical history
your medication
blood sugar risk
blood pressure
history of eating disorder or disordered eating
weight loss goals
current calorie intake
protein intake
hydration
side effects
mental wellbeing
whether weight loss medication is affecting appetite too strongly
Without supervision, people may not realise when fasting has become unsafe.
Red flags include:
dizziness
fainting
shaking
palpitations
low mood
irritability
binge eating
obsessive thoughts about food
feeling scared to eat
avoiding meals socially
worsening nausea
constipation
dehydration
very low energy
inability to meet protein needs
If any of these happen, the fasting pattern should be stopped or reviewed
Intermittent fasting and weight management medication
If you are using weight management medicines, such as GLP-1 or GIP/GLP-1 treatments, intermittent fasting needs even more caution.
These medicines can reduce appetite and make people feel full more quickly. Some patients already find it difficult to eat enough, especially during the early weeks of treatment or after a dose increase.
Adding fasting on top may increase the risk of:
eating too little
nausea
dehydration
constipation
low energy
inadequate protein intake
poor nutrition
loss of muscle mass
worsening side effects
becoming overly restrictive
At Aster, we would not encourage patients to use intermittent fasting as a way to push faster weight loss while on treatment.
The goal is not to eat as little as possible. The goal is to lose weight safely while protecting health, strength, digestion, mood and long-term habits.
Does intermittent fasting work?
For some people, intermittent fasting may help reduce overall calorie intake. But it is not magic, and it is not automatically better than other approaches.
Weight loss still depends on overall energy balance, meal quality, activity, sleep, stress, hormones, medication, health conditions and consistency.
Some people do well with a gentle overnight eating structure, such as avoiding late-night snacking. Others do much better with regular meals and snacks.
Both can be valid.
The right approach is the one that supports your health without making eating feel more stressful or obsessive.
How Aster can support safer weight management
Aster provides online weight management support from a GPhC-registered pharmacy team. Our focus is on safe, clinically reviewed care, not extreme dieting.
We support patients with:
suitability checks before treatment
ongoing monitoring
side effect guidance
nutrition basics
hydration and fibre advice
treatment reviews
realistic weight loss expectations
signposting when additional support is needed
We do not encourage patients to chase rapid results through unsafe restriction. Medical weight management should be structured, monitored and realistic.
This article is for general information only and does not replace medical advice. Weight loss medicines are prescription-only and may not be suitable for everyone. Decisions about continuing, reducing or stopping treatment should be made with an appropriate clinician based on your individual circumstances.
This article was written by Sally
Operations Manager
Aster, Pharmacy Clinic Edinburgh & Arcadia Health Clinic
