Why is there a diet before a gastric sleeve?

A few weeks before your gastric sleeve, your care team asks you to change how you eat. It can feel like a test of willpower right before a big day. It is really a medical step, with a clear reason: your liver.

Why the liver matters

Your liver sits just above and in front of your stomach. Fatty liver disease is common in people living with obesity: fat builds up in the liver, which makes it bigger and heavier. During a sleeve, the surgeon has to lift the liver gently to reach the stomach. A large, heavy liver is harder to move and can make the operation more difficult.

A short diet that is low in calories, sugar and starch makes the liver smaller, often within about two weeks. That gives your surgeon more room to work.

What studies show

• Canadian guidelines note that a low-calorie diet that is low in carbohydrates may shrink the liver by up to 19%.
• A review of nine studies found that the liver got 5% to 20% smaller, and that people lost about 3 to 15 kg (about 6 to 33 lb) before surgery.
• In an Australian study that measured the liver with scans, about 80% of the drop in liver size happened in the first two weeks of the diet.
• In a European trial of 298 people having a gastric bypass, surgeons rated the operation as less difficult after a two-week diet, and there were fewer complications in the first month.

Not every study agrees about complications. The review of nine studies found no clear drop in complications overall. So the main proven benefits are a smaller liver and an operation that is easier to do.

What it usually looks like

Canadian guidelines describe a liquid-based, low-calorie diet for two to three weeks before surgery, often with protein shakes that add up to about 650 to 900 calories a day. Plans differ between programs and between people. At 360 Sleeve, your dietitian sets your plan with you.

• Low in calories, sugar and starch, with enough protein.
• Often a liquid meal replacement or protein shakes for some or all meals.
• Plenty of fluids, mostly water and other drinks without sugar.
• Sometimes small amounts of low-starch vegetables, such as lettuce, spinach or cucumber.
• Clear fluids only for the last day or two, if your team asks you to.

The diet also gives you a head start on habits you will use after surgery: sipping fluids through the day, planning meals and putting protein first.

If you take medicines

A sudden drop in calories changes how some medicines work. Canadian guidelines say people with diabetes need to check their blood sugar closely during the diet and get clear instructions on adjusting their diabetes medicines, because the need for some of them, such as insulin, can drop a lot. Blood pressure medicines and water pills may need changes too.

Never stop or change a prescribed medicine on your own. Ask your team for a written plan before the diet starts.

Tips for getting through it

• Plan your shakes and drinks for the whole day, so hunger does not catch you off guard.
• Move tempting foods out of easy reach, and tell the people you live with what support you need.
• Keep busy at your usual mealtimes, with a walk, a call or a hobby.
• If you slip, do not give up. Tell your dietitian, and start again with your next shake or meal.

Mild side effects that pass with time can happen on this kind of diet. Tell your dietitian honestly how it is going. If something is not working, your team would rather know, so they can help.