Some foods raise blood sugar far more than others, and a high rise in blood sugar after meals can increase risk for diabetes, heart attacks and premature death. A study from Israel shows that some people develop surprisingly high blood sugar levels after eating foods such as bread, pizza, potato, tomatoes or bananas, while others do not develop the expected rise in blood sugar even after drinking a sugared soft drink or eating a cookie (Cell, published online November 19, 2015;163(5):1079–1094). The authors believe that by knowing which foods cause a person’s highest rises in blood sugar, they could personalize a diet to lower the rise in blood sugar that follows eating.
More than 800 people wore blood sugar monitors for a week. They used a smart phone app to keep track of their sleeping, exercising and eating. They also provided stool samples to measure the type and amount of bacteria in their intestines.
Different people had different blood-sugar responses when they ate the same foods. For example, some people spiked very high blood sugars after eating tomatoes, while others had very low blood sugar responses to tomatoes. Bread produced an average blood sugar rise of 44 milligrams per deciliter with a range as low as 15 and as high as 79.
The researchers gave their test subjects diets full of foods that caused either very high or very low blood sugar responses. They found that their subjects had very different blood sugar responses to these diets. Important factors that predicted that their blood sugar levels would rise very high after eating certain foods included:
• excess body fat content
• older age
• increased susceptibility to diabetes
• extreme sleep patterns (too much or too little)
• lack of exercise
• high blood pressure
• high cholesterol levels
• high blood insulin levels
• having certain types of bacteria in their intestines
Based on their findings, the researchers developed personalized diets for 26 of their subjects and showed that the diets reduced their blood sugar levels after meals and altered their gut bacteria.
How Gut Bacteria Influence Risk for Diabetes
The bacteria in your intestines change when you change your diet. The bacteria in your colon live on the same food that you eat. After you eat, some of the food is broken down and absorbed in your upper intestines, while some passes unabsorbed to your colon where your gut bacteria can break down the leftovers. If you change from a diet full of meat, dairy and sugar to a high-plant diet, the amount and types of bacteria in your colon change dramatically in JUST ONE DAY (Nature, December 11, 2013). One day after dropping meat from their diets, people had colon bacteria that started to return to those promoted by a vegan diet. Adding meat back in to a vegan diet caused an immediate increase in the bacteria (Bilophila wadsworthia, Alistipes putredinis and species in the genus Bacteroides) that grow with exposure to bile, which increases when a person eats more fat. These bacteria convert fat and fiber to short-chain fatty acids, which is usually beneficial, but some of these bacteria have been shown to cause inflammation that can increase risk for diabetes and cause plaques to form in arteries.
You can consume beneficial bacteria found in live-culture yogurt and in some supplements, but these bacteria stay in your gut only as long as you continue to take the yogurt or supplements. When you stop eating these bacteria, they disappear from your colon; they do not continue to multiply. Eat yogurt if you enjoy it, but if you want to improve your gut bacteria, I recommend that you save your money and eat a primarily plant-based diet that will nurture a permanent colony of beneficial bacteria.
What Should This Study Mean for You?
I found this study interesting but I fear that its authors will try to convert it into yet another fad diet, when all they have really told you is what we already know about risk for diabetes. You are at increased risk for high blood sugar rises after meals, diabetes, heart attacks and premature death if you have:
• excess fat stored in your belly (pinch more than 3″ of fat under the skin on your belly)
• very narrow and small buttocks
• lack of exercise
• excess weight
• high blood pressure (systolic > 120 before you go to sleep at night)
• high bad LDL cholesterol (>100)
• low good HDL cholesterol (<40)
• high fasting blood insulin level (>10)
• excess sugar stuck on cells (HbA1c> 5.5)
• high fasting blood sugar (>95)
• a fatty liver (diagnosed with a very safe and inexpensive sonogram of your liver)
If you have none of these risk factors, thank your parents and continue your intelligent lifestyle.
If you have any of the risk factors for diabetes, try to:
• avoid sugared drinks, sugar-added foods, fried foods, red meat and processed meats
• restrict refined carbohydrates including bakery products and pastas
• eat lots of fruits and vegetables
• try to exercise every day
• lose weight if overweight
• keep hydroxy vitamin D blood levels above 50 nmol/L
If you cannot lower your blood pressure, cholesterol and blood sugar with these lifestyle changes, check with your doctor about options for further treatment.