Gastric sleeve pre-op diet: the liver shrinking diet explained

The liver sits directly over the upper part of the stomach. In people living with obesity it is often enlarged, heavy and stiff, because it stores extra fat and a form of sugar called glycogen. During a sleeve gastrectomy the surgeon has to lift the liver out of the way to work on the stomach.

A large, stiff liver is hard to move. It makes the operation more difficult, it raises the risk of surgical complications, and in some cases the surgeon has to switch from keyhole surgery to open surgery, which means a bigger scar, a longer recovery and more risk. NHS bariatric services explain that the aim of the pre-op diet is to shrink and soften the liver so that keyhole surgery is possible.

The diet has a second benefit. It is your first experience of eating very differently, with small portions, more protein and fewer sugary foods, which is the pattern you will follow for life after the sleeve.

The diet is very low in calories and low in carbohydrates. When you eat this way, the body uses up the glycogen stored in the liver for energy. Glycogen is stored together with water, so as it is used the liver loses water and starts to shrink and soften quickly. Over the following days the body also starts to draw on the fat stored in and around the liver.

Randomised trials have found that a short low-calorie diet before bariatric surgery reduces liver size. That is why the diet has to be strict right up to the day of surgery: one large meal can refill the liver's glycogen and undo much of the effect.

Most teams ask for a couple of weeks. Some ask for longer, especially for people with a higher body mass index or a larger liver, and a few start with a longer period of gentler weight loss before the strict phase. Your surgical team will give you an exact start date. Count back from your operation day, and do not start late or stop early.

Hospitals use a few versions of the same idea. They all keep calories, sugar, starch and fat very low and protein moderate.

Liquid diet

The strictest version. You have only liquids for the whole period: skimmed or semi-skimmed milk, meal replacement shakes, smooth soups, low-fat yoghurt drinks and sugar-free jelly, plus water and other calorie-free drinks. Many teams prefer it because portion sizes are easy to control.

Meal replacement diet

You replace most meals with specially formulated shakes or soups and have one small meal a day, usually lean protein such as grilled chicken or white fish with green vegetables or salad.

Calorie-controlled food plan

A food-based plan with small portions of lean protein, plenty of non-starchy vegetables and very little bread, pasta, rice, potatoes, sugar or fat. It is less common, because it is harder to keep the calories low enough, and some teams only offer it when a liquid plan is not suitable.

Exactly what is allowed depends on your plan, but these are typical:

• Skimmed or semi-skimmed milk, within the amount your plan allows
• Meal replacement shakes or soups recommended by your team
• Low-fat, low-sugar yoghurt
• Sugar-free jelly
• Clear soups and stock
• Lean protein such as skinless chicken, turkey, white fish, eggs or tofu, if your plan includes a meal
• Non-starchy vegetables and salad: leafy greens, broccoli, cauliflower, courgette, peppers, cucumber, tomato, mushrooms
• Water, tea, coffee and sugar-free squash, with any milk counted in your allowance
• A complete multivitamin and mineral supplement, if your team recommends one

• Sugar, sweets, chocolate, cakes and biscuits
• Bread, pasta, rice, potatoes, cereals and other starchy foods
• Fried, fatty or creamy foods, including cheese and processed meats
• Fruit juice, smoothies and sugary fizzy drinks
• Alcohol
• Snacks between meals that are not part of your plan
• Sweetcorn, peas and other starchy vegetables, unless your plan says otherwise

Fizzy drinks are worth giving up now even if they are sugar-free, because carbonated drinks are usually off the menu after sleeve surgery too.

This is an example of how a liquid plan can be spread across a day. Your team's plan sets the actual amounts.

• Breakfast: a meal replacement shake, or a glass of milk from your allowance
• Mid-morning: tea or coffee with milk from your allowance, and water
• Lunch: a meal replacement soup, or a glass of milk with sugar-free jelly
• Afternoon: a low-fat yoghurt drink if allowed, and water
• Dinner: a meal replacement shake or soup, or a small portion of grilled chicken or fish with green vegetables if your plan includes one meal
• Evening: sugar-free jelly and a calorie-free drink

Spread your allowance evenly through the day rather than saving it for the evening. Long gaps make hunger, headaches and dizziness worse.

The first few days are usually the hardest. Common side effects include:

• Hunger and cravings: they tend to ease after the first few days. Keep busy, sip water and keep tempting food out of sight.
• Headaches, tiredness and feeling light-headed: often linked to the sudden drop in carbohydrates and to not drinking enough. Drink plenty of calorie-free fluids, stand up slowly and avoid strenuous exercise.
• Constipation: more likely on a liquid plan with little fibre. Drink plenty of water and ask your team or pharmacist if a gentle remedy is needed.
• Loose stools or stomach cramps: sweeteners in sugar-free products can cause them in some people.
• Low mood or irritability: common when your usual eating habits change. Tell the people around you what you are doing and ask for their support.

If you feel very unwell, faint, or cannot keep fluids down, contact your surgical team or a doctor.

Tell your team about every medicine you take, including blood pressure tablets, blood thinners and weight loss injections. Some may need to be changed or paused before surgery, and only your doctors should make that decision.

One slip will not usually cancel your operation, but it can undo part of the effect, especially close to the surgery date. A large or high-carbohydrate meal can refill the liver with glycogen and water, leaving it bigger and stiffer than it should be.

If your liver is still too large on the day, the operation can be more difficult, the surgeon may need to convert to open surgery, and in some cases it may be postponed. The answer is not to hide it: if you have had a bad day, get back on the plan straight away and tell your team honestly. They would rather know.

Avoid a last big meal before surgery. It is a tempting idea, but it works directly against the diet.

Most people lose some weight on the pre-op diet, and a good part of it in the first days is water released as the liver's glycogen is used up. The amount varies from person to person. The number on the scale is a bonus, not the point: the goal is a smaller, softer liver on the day of your operation.

Keep to the diet until your hospital tells you to stop eating and drinking. You will be given fasting instructions for the hours before the operation, usually with a time after which you can have only clear fluids and a time after which you must have nothing at all. Follow your own hospital's instructions exactly, because they differ between hospitals and anaesthetists.

If you are having your gastric sleeve in Turkey or another country, the pre-op diet starts at home, before you travel. A little planning helps:

• Ask your clinic for its pre-op diet plan in writing as soon as your date is set, and check whether it wants you on a liquid plan or a food-based plan.
• Buy your shakes or soups before you start, and plan how you will keep to the diet on the travel day and at the hotel.
• Send your clinic a full list of your medicines, and ask how to adjust any diabetes treatment.
• Keep a short diary of what you eat and drink, so you can show your surgeon you followed the plan.

You can read more about the operation itself on our gastric sleeve surgery page, and our guide to gastric sleeve vs gastric bypass explains how the two operations compare. Bypass patients follow a similar liver shrinking diet before gastric bypass surgery.

The pre-op diet ends on the day of surgery, but careful eating does not. After a sleeve you move gradually from clear liquids to full liquids, then to puréed and soft food, and finally to normal textures over several weeks. Our guide to the stages of the gastric sleeve diet walks through each stage, and our gastric sleeve recipes help once you are back on solid food. It is also worth reading how to prevent dumping syndrome before you start eating normally again.