RecruitingInterventional

Does synbiotic supplementation improve the effects of a ketogenic diet?

This study wants to find out if a special supplement, called a synbiotic, can help people on a ketogenic diet avoid a common side effect: a rise in "bad" cholesterol. A ketogenic diet involves eating very few carbohydrates and is popular for weight loss and blood sugar control. However, it can sometimes increase LDL cholesterol, which isn't good for your heart over time. We believe this might be linked to changes in gut bacteria. We're testing if taking a synbiotic daily (which combines good bacteria and fibre) can keep your gut healthy and stop your cholesterol from rising. If it works, it could make ketogenic diets safer and more beneficial for many people. We're looking for healthy adults aged 18-65 to take part for about 14 weeks.

At a glance

Status

Recruiting

Sponsor

University of Bath

Enrolment target

Start

01 Feb 2026

Estimated completion

30 Dec 2027

Hypercholesterolaemia

What is this study about?

Many people are interested in ketogenic diets, where you drastically cut down on carbohydrates (like sugars and starches) to less than 50g a day. When you do this, your body starts to burn fat for energy and produces special molecules called ketones. People follow ketogenic diets for different reasons, such as managing their weight, controlling blood sugar, or even for potential benefits to their brain.

While ketogenic diets can be helpful for some, one possible concern is that they can sometimes lead to an increase in LDL cholesterol. This is often called "bad" cholesterol because, over many years, high levels can increase your risk of heart problems. Our research suggests that this rise in cholesterol might be connected to changes in the tiny living things, like bacteria, that live in your gut.

This study, called SynKeto, aims to see if taking a daily supplement, known as a synbiotic, can help. A synbiotic is a combination of good bacteria (probiotics) and special fibres (prebiotics) that feed these good bacteria. We want to find out if this supplement can keep your gut bacteria healthy and, in turn, prevent the typical increase in "bad" cholesterol that can happen when someone starts a ketogenic diet. If successful, taking a synbiotic could allow people to enjoy the potential benefits of a ketogenic diet while reducing the risks linked to higher cholesterol.

Key takeaways

The study investigates if a synbiotic supplement can prevent high cholesterol on a ketogenic diet.
A ketogenic diet limits carbohydrates to encourage fat burning for energy.
High 'bad' cholesterol (LDL) can be a side effect of a ketogenic diet.
Synbiotics combine good gut bacteria (probiotics) and the fibre that feeds them (prebiotics).
The study involves dietary changes, daily supplements, and several check-up visits over 14 weeks.
Participants will receive financial compensation and personal health results.

Who may be eligible?

We are looking for around 64 healthy men and women aged between 18 and 65 years old to join this study. You should generally be in good health, without any ongoing serious medical conditions or strict dietary needs.

There are certain things that would mean you can't take part. For example, if you already have conditions like Type 1 or Type 2 diabetes, severe high blood pressure, or if you've recently used antibiotics (in the last 3 months). We also can't include you if you're taking medicines that lower your cholesterol, or if you already regularly use certain supplements like probiotics or laxatives. If you're pregnant, planning to become pregnant, or have gone through menopause, you also won't be able to join. We need participants who are not already following a low-carbohydrate ketogenic diet and whose weight has been stable for the past three months. Vegetarians and vegans cannot take part due to dietary requirements of the study.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you between 18 and 65 years old?
Do you have a healthy weight for your height (BMI between 20.0 and 34.9)?
Are you generally healthy and do not have major medical conditions like diabetes or severe high blood pressure?
Have you avoided antibiotics in the last 3 months?
Are you not currently pregnant, planning to be, or have you gone through menopause (for women)?
Are you not already regularly following a low-carbohydrate or ketogenic diet?

Answer every question to see your result.

What does participation involve?

If you decide to take part, your involvement will last for about 14 weeks in total. This includes a 12-week period where you'll be asked to follow a ketogenic diet and take a daily supplement. First, you'll have an initial visit to check if you're suitable for the study. If you are, and you agree to continue, you'll sign a consent form and we'll give you equipment to track your diet, physical activity, and your sugar and ketone levels.

About one to two weeks later, you'll have your first main visit. This involves various checks including blood, fat, and stool samples, and body scans to see your body's make-up. After this, you'll start the 12-week main part of the study, following the ketogenic diet and taking your daily supplement. Neither you nor the research team will know if you're taking the active synbiotic or a dummy pill (placebo) during this time. Halfway through, at 6 weeks, you'll have an interim visit for more blood and stool samples, body scans, and checks on your activity and levels of sugar and ketones. Finally, at the end of the 12 weeks, you'll have a last visit, similar to your first main visit.

Potential risks and benefits

By taking part, you'll be contributing valuable information that could help us understand how ketogenic diets affect cholesterol, and if a synbiotic can prevent cholesterol from rising. This research could potentially benefit many people who use ketogenic diets and the doctors who advise them. You'll also receive payments for your travel and parking, a contribution towards your grocery costs for the 12 weeks, and a £200 gift voucher upon completing the study. Within 2-4 weeks of finishing, you’ll get a summary of your personal results, including information on your diet, physical activity, blood pressure, body composition, and thinking skills. As for risks, any changes to your diet can have effects, and taking supplements might have side effects, though synbiotics are generally considered safe. You are free to withdraw from the study at any time without giving a reason.

Locations (1)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

GP practices across BANES and Wiltshire
City only
-, England

Common questions

What is a ketogenic diet?

A ketogenic diet means eating very few foods containing carbohydrates (like bread, pasta, sugary drinks), usually less than 50g per day. This makes your body burn fat for energy.

What is 'bad cholesterol' (LDL cholesterol)?

LDL cholesterol is often called 'bad cholesterol' because, in high amounts over time, it can build up in your arteries and increase your risk of heart disease.

What is a synbiotic?

A synbiotic is a supplement that combines good bacteria (probiotics) with special dietary fibres (prebiotics) that help these good bacteria grow in your gut.

How long will I be involved in the study?

Your involvement in the study will be for about 14 weeks in total, which includes a 12-week period where you'll follow the diet and take the supplement.

Will I know if I'm taking the synbiotic or a dummy pill?

No, neither you nor the research team will know if you're taking the active synbiotic or a dummy pill (placebo) during the 12-week intervention period. This helps ensure the study results are fair.

How to find out more

Lucy Rogers

lr2013@bath.ac.uk - Official trial record

Always speak to your GP or specialist before deciding to take part in a study.