Possible side effects of a Very Low Calorie Diet (VLCD)

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Possible side effects of a Very Low Calorie Diet (VLCD)

Possible side effects of a Very Low Calorie Diet (VLCD)

As with any medical or dietary treatment, following a VLCD may cause some side effects or temporary symptoms as your body adjusts. These effects are usually mild and short-lived, but it’s important to be aware of them and to report any that persist or cause concern to your GP. 

Possible side effects include:

You will also be provided with practical tips on preventing and managing these side effects during throughout the TDR phase. Your Diabetes Practitioner is also there to support you, with assistance from our clinical team as needed. 

Very common

Headaches, light-headedness, dizziness

Fatigue, low energy, irritability

Cramps

Constipation, diarrhoea, bloating, flatulence

Feeling cold, tingling fingertips and toes

Bad breath, dry mouth

Hunger

Common

Nausea, heartburn, indigestion

Mood swings, poor concentration

Temporary blurred vision

Hair loss

Dry skin

Menstrual irregularities

Fluctuations in blood glucose and blood pressure levels – These will be monitored during the programme, and your GP will be informed of any readings that may require attention

Occasional

Gallstones – Rapid weight loss and fat breakdown can increase the risk of developing gallstones. If you already have gallstones, following a very low-calorie diet (VLCD) may worsen existing symptoms.  If you develop new gallstone symptoms or have a flare-up while on TDR, please inform your GP and your Diabetes Practitioner or our Patient Support Team as soon as possible. 
For more information, see the section “Rapid Weight Loss and Gallbladder Health” at the end of this document.

Disordered Eating – If you have a current diagnosis of an eating disorder, you will not be eligible for the programme. If you have experienced disordered eating in the past, following a VLCD may increase the risk of these patterns returning. Please speak to your GP or Diabetes Practitioner if you have any concerns.

Rare / serious

Ketoacidosis – If you are required to make medication changes when starting VLCD, make sure these are made as instructed by your GP on the same day you start VLCD. You should not take SGLT2 inhibitors, meglitinides, sulfonylureas or insulin while following a VLCD

Allergic reaction – If you have any allergies, make sure you read the Total Diet Replacement (TDR) product labels before consuming. If you don’t have any known allergies to any of the ingredients, make sure you try the sample pack before starting VLCD to make sure that you can tolerate the TDR products

Refeeding syndrome – While on VLCD make sure you consume your TDR products according to instructions. Since the diet is already very low in calories, you should not consume fewer TDR products than advised. If you are struggling with your TDR intake, please inform your Diabetes Practitioner or our Patient Support Team

If you experience any side effects that cause concern while on VLCD report them to your GP / medical team / A&E depending on severity. Remember to prioritise the advice received from them and to let your Diabetes Practitioner or our Patient Support Team know as soon as possible so next steps can be discussed regarding the programme.   

Rapid Weight Loss and Gallbladder Health

Rapid weight loss can have significant benefits for people with type 2 diabetes, but it can also affect your gallbladder. Please read this guide carefully to help you make an informed decision before starting the programme. 

What is the gallbladder? 

The gallbladder is a small organ located under the right side of your ribcage. It stores bile, a digestive fluid that helps break down fats. Problems with the gallbladder are sometimes called biliary disease, which can include gallstones and inflammation. 

How rapid weight loss can affect the gallbladder 

During the TDR phase of the programme, rapid weight loss (more than 2 lb or 1 kg per week) may occur. While long-term weight loss generally reduces the risk of gallstones, rapid weight loss can temporarily increase the risk: 

Rapid weight loss can make gallstones more likely to form. 
If you already have gallstones but don’t experience symptoms, rapid weight loss may worsen them and trigger symptoms. 
Gallstones can move from the gallbladder into the bile duct, causing a blockage. This can lead to severe abdominal pain, nausea, and vomiting. In some cases, it can cause pancreatitis (inflammation of the pancreas). 
In some cases, this can lead to infection of the gallbladder (acute cholecystitis) or bile duct (cholangitis). These are medical emergencies requiring hospital treatment. If untreated, cholecystitis can cause the gallbladder to rupture.

There are few studies measuring the risk of biliary disease during very low‑calorie diets. One study found that about 1 in 10 people developed gallstones after a 16‑week very‑low‑calorie diet¹. This risk is similar to that seen with medically supervised weight‑loss injections, such as Wegovy, Ozempic, or Mounjaro².

Knowing your risk

People with a higher starting weight, greater weight loss, or elevated blood triglycerides (a type of fat in the blood) are at increased risk of developing biliary disease.

In some cases, ursodeoxycholic acid, a prescription medication, may be used to reduce gallstone formation. However, there is limited evidence to support its use ³.

If you are unsure whether you are at high risk, or if you already have a diagnosis of gallstones, discuss this with your GP. Together, you can decide whether proceeding with a very low calorie diet, or trying a slower weight loss approach, is best for you.

Symptoms to look out for

Right-sided abdominal pain, sometimes spreading toward the shoulder. This may be worse after eating or taking your TDR products. In some cases, pain may be felt across the whole abdomen. 
Pain may occur with or without nausea, vomiting, or fever.

What to do if you develop symptoms

Stop your TDR immediately and eat normal food if tolerated. 
Contact your GP to arrange an appointment. 
Inform your Diabetes Practitioner so we can advise on the next steps for the programme.

If pain is severe, you have a fever, or are vomiting, seek urgent medical help (visit A&E or call 999).

If gallstone symptoms occur during the TDR phase, you will need to stop TDR. Our clinical team will advise on the safest next steps, which may include continuing the programme with healthy eating support or, in some cases, discharge. 

Making an informed choice

Rapid weight loss can be an effective step in managing type 2 diabetes, but it is important to understand the risks. Discuss your options with your GP or diabetes team, and consider all available weight loss strategies to choose the safest approach for you. 

Sources:

¹ Yang H, Petersen GM, Roth MP, Schoenfield LJ, Marks JW. Risk factors for gallstone formation during rapid loss of weight. Digestive Diseases and Sciences. 1992; 37(6):912-8. doi: 10.1007/BF01300390

² He L, Wang J, Ping F, et al. Association of Glucagon-Like Peptide-1 Receptor Agonist Use With Risk of Gallbladder and Biliary Diseases: A Systematic Review and Meta-analysis of Randomized Clinical Trials. JAMA Internal Medicine. 2022;182(5):513–519. doi:10.1001/jamainternmed.2022.0338

³BMJ Best Practice (2024) Cholelithiasis (gallstones). BMJ Publishing Group. Available at: https://bestpractice.bmj.com/topics/en-gb/3000015 (Accessed: 23 October 2025). 