Question
A 44-year-old woman attends a routine workplace health review. A random blood glucose level is mildly elevated. She has obesity, with a BMI around 38 kg/m², but is otherwise well and takes no regular medicines.
She wants to try lifestyle and dietary measures before considering tablets. She is advised to reduce foods that cause a rapid rise in post-meal blood glucose and is scheduled for formal diabetes testing later.
Which of the following foods is the best example of something she should avoid?
a. Boiled baby potatoes
b. Wholegrain brown rice
c. Oat-based digestive biscuits
d. Peanuts
e. White bread
Answer
e. White bread
Detailed explanation
This question is testing the glycaemic index, or GI.
The glycaemic index measures how much a carbohydrate-containing food raises blood glucose compared with pure glucose. Glucose has a GI of 100 by definition.
Foods are usually classified approximately as:
- Low GI: 55 or less
- Medium GI: 56–69
- High GI: 70 or more
White bread has a high glycaemic index, around 80, so it causes a rapid rise in blood glucose after eating. Therefore, in a patient with impaired glucose regulation, obesity, or risk of type 2 diabetes, white bread is a classic food to reduce or avoid.
The key idea is not simply “sweet food = high GI”. Some foods that do not taste very sweet, such as white bread, white rice, and baked potato, can have a high GI because their starch is rapidly digested and absorbed.
Why the other options are wrong
a. Boiled baby potatoes
Boiled new potatoes have a medium GI, around 62. This is important because potato GI depends strongly on preparation. Baked potatoes have a high GI, but boiled new potatoes are not as high.
b. Wholegrain brown rice
Brown rice has a medium GI, around 58. It is generally better than white rice, which has a high GI, around 87. Brown rice contains more fibre and is absorbed more slowly.
c. Oat-based digestive biscuits
Digestive biscuits may sound sugary and unhealthy, but their GI is usually medium, around 59. They are not the best answer when compared with white bread. This is a classic exam trap: “sugary-sounding” does not always mean highest GI.
d. Peanuts
Peanuts are low carbohydrate and have a low GI. They do not cause a major glucose spike. They may be calorie-dense, but that is a different issue from glycaemic index.
e. White bread
White bread has a high GI, around 80. It is rapidly digested and absorbed, causing a sharp post-prandial glucose rise. This is the correct answer.
Key exam point
White bread, white rice, and baked potato are high-GI foods; brown rice, boiled new potatoes, porridge, couscous, and digestive biscuits are generally medium GI; peanuts and most fruit/vegetables are low GI.
Very important concept / clinical trap
Do not confuse glycaemic index with sugar content, calories, or “healthy-sounding” food labels. GI is about the speed and degree of blood glucose rise after eating carbohydrate. A food can taste non-sweet but still have a high GI, such as white bread or baked potato. A food can be calorie-dense but low GI, such as peanuts.
Cheat sheet for exam
- Glycaemic index = ability of food to raise blood glucose compared with glucose.
- Glucose has GI 100.
- High GI: 70 or more.
- Medium GI: 56–69.
- Low GI: 55 or less.
- White bread = high GI, around 80.
- White rice = high GI, around 87.
- Baked potato = high GI, around 85.
- Boiled new potato = medium GI, around 62.
- Brown rice = medium GI, around 58.
- Digestive biscuit = medium GI, around 59.
- Porridge = medium GI, around 55.
- Peanuts = low GI because they contain little carbohydrate.
- High-GI foods cause rapid post-prandial hyperglycaemia.
- High-GI diets are associated with obesity and increased risk of type 2 diabetes.
- GI can be affected by cooking method, processing, fibre content, fat/protein content, and fruit ripeness.
- More processed starch usually means higher GI.
- Wholegrain foods usually have lower GI than refined versions.
- Baked potato has higher GI than boiled new potato.
- Brown rice is preferable to white rice for glycaemic control.
- In exams, white bread is a classic high-GI answer.
Flash cards
Q: What does glycaemic index measure?
A: It measures how much a food raises blood glucose compared with glucose.
Explanation: Glucose is given a GI of 100, and other foods are ranked relative to it.
Q: What GI value defines a high-GI food?
A: Usually 70 or above.
Explanation: High-GI foods cause rapid post-prandial glucose rises.
Q: What is the classic high-GI bread example?
A: White bread.
Explanation: White bread has a GI around 80 due to rapidly digestible refined carbohydrate.
Q: Is brown rice high or medium GI?
A: Medium GI.
Explanation: Brown rice has more fibre and slower absorption than white rice.
Q: Is white rice high or medium GI?
A: High GI.
Explanation: White rice is rapidly digested and has a GI around 87.
Q: Are peanuts high GI?
A: No, they are low GI.
Explanation: Peanuts contain little carbohydrate, so they cause little glucose rise.
Q: Why is baked potato higher GI than boiled new potato?
A: Cooking method changes starch structure and digestibility.
Explanation: Baked potato is more rapidly digested and has a higher GI.
Q: What is a common exam trap in GI questions?
A: Choosing a sweet-sounding food instead of a refined starch.
Explanation: Digestive biscuits may sound sugary, but white bread has a higher GI.
Q: What clinical problem is associated with high-GI diets?
A: Obesity and increased type 2 diabetes risk.
Explanation: Repeated post-prandial glucose spikes worsen metabolic risk.
Q: What factors can alter GI?
A: Cooking method, processing, ripeness, fibre, fat, and protein content.
Explanation: GI is not fixed purely by the food name.
MCQs
- A 50-year-old man with impaired fasting glucose asks which food is most likely to cause a rapid post-meal glucose rise. Which is the best answer?
a. Peanuts
b. White bread
c. Brown rice
d. Boiled new potatoes
e. Lentils
Answer: b. White bread
Explanation: White bread is a high-GI food, with a GI around 80. It is made from refined carbohydrate and is rapidly digested. Peanuts and lentils are low GI, while brown rice and boiled new potatoes are generally medium GI.
- Which of the following is false regarding glycaemic index?
a. Glucose has a GI of 100
b. High-GI foods may worsen post-prandial hyperglycaemia
c. Peanuts are high GI because they contain a lot of fat
d. Cooking method can affect GI
e. White rice has a higher GI than brown rice
Answer: c. Peanuts are high GI because they contain a lot of fat
Explanation: This statement is false. Peanuts are low GI because they contain relatively little carbohydrate. Fat content affects calories, but GI mainly reflects blood glucose response to carbohydrate-containing foods. White rice is high GI, brown rice is medium GI, and cooking method can significantly alter GI.
- Which food is correctly paired with its approximate glycaemic index category?
a. White bread — low GI
b. Peanuts — high GI
c. Brown rice — medium GI
d. White rice — low GI
e. Baked potato — low GI
Answer: c. Brown rice — medium GI
Explanation: Brown rice has a medium GI, around 58. White bread, white rice, and baked potato are high-GI foods. Peanuts are low GI because they are low in carbohydrate.
- A patient with obesity and borderline diabetes is advised to switch from a high-GI staple food to a lower-GI alternative. Which substitution is most appropriate?
a. Brown rice instead of white rice
b. White bread instead of porridge
c. Baked potato instead of boiled new potato
d. White rice instead of lentils
e. Cornflakes instead of oats
Answer: a. Brown rice instead of white rice
Explanation: Brown rice has a lower GI than white rice because it is less refined and contains more fibre. White rice is a classic high-GI food. Baked potato has a higher GI than boiled new potato, and white bread is higher GI than porridge.
- Which of the following foods is most likely to have a high glycaemic index?
a. Peanuts
b. Most non-starchy vegetables
c. Baked potato
d. Brown rice
e. Digestive biscuit
Answer: c. Baked potato
Explanation: Baked potato has a high GI, around 85. Boiled new potatoes have a medium GI, showing that preparation method matters. Peanuts and most non-starchy vegetables are low GI, while brown rice and digestive biscuits are medium GI.
- Which of the following is the best explanation for why white bread has a high GI?
a. It contains no carbohydrate
b. It is rich in unsaturated fat
c. It contains slowly absorbed fibre-rich carbohydrate
d. It contains refined starch that is rapidly digested
e. It contains mainly protein
Answer: d. It contains refined starch that is rapidly digested
Explanation: White bread is made from refined flour. Its starch is rapidly broken down and absorbed, producing a sharp glucose rise. This is why white bread is a classic high-GI food.
- Which of the following is false?
a. GI can be affected by fruit ripeness
b. GI can be affected by food processing
c. GI can be affected by cooking method
d. GI is identical to total calorie content
e. GI describes blood glucose response after eating
Answer: d. GI is identical to total calorie content
Explanation: GI is not the same as calorie content. GI measures the blood glucose response to carbohydrate-containing food. Peanuts, for example, are calorie-dense but low GI. Cooking, ripeness, and processing can all alter GI.
- A dietician explains GI to a patient. Which statement is most accurate?
a. GI measures how salty a food is
b. GI measures the blood glucose rise compared with glucose
c. GI measures LDL cholesterol response to a food
d. GI measures total daily calorie intake
e. GI only applies to foods that taste sweet
Answer: b. GI measures the blood glucose rise compared with glucose
Explanation: Glycaemic index compares the blood glucose response after eating a food with the response after consuming glucose. Glucose is assigned a GI of 100. GI does not measure salt, LDL cholesterol, calories, or sweetness.
- Which option contains only high-GI examples?
a. Peanuts and lentils
b. Brown rice and porridge
c. White bread and baked potato
d. Boiled new potato and digestive biscuit
e. Vegetables and peanuts
Answer: c. White bread and baked potato
Explanation: White bread and baked potato are both high-GI foods. Brown rice, porridge, boiled new potatoes, and digestive biscuits are generally medium GI. Peanuts and many vegetables are low GI.
- A patient asks why white rice is less suitable than brown rice for glycaemic control. Which answer is best?
a. White rice has less rapidly absorbable carbohydrate
b. Brown rice has a higher GI than white rice
c. White rice has a higher GI due to more refined carbohydrate
d. Brown rice contains no carbohydrate
e. White rice is low GI because it is not sweet
Answer: c. White rice has a higher GI due to more refined carbohydrate
Explanation: White rice is more refined and has a higher GI than brown rice. Brown rice contains carbohydrate but is absorbed more slowly because of its fibre and less processed structure.
- Which of the following is a medium-GI food?
a. White bread
b. White rice
c. Baked potato
d. Brown rice
e. Peanuts
Answer: d. Brown rice
Explanation: Brown rice is medium GI, around 58. White bread, white rice, and baked potato are high GI. Peanuts are low GI.
- Which of the following clinical consequences is most associated with frequent high-GI food intake?
a. Reduced post-prandial glucose excursions
b. Increased risk of obesity and type 2 diabetes
c. Immediate hypoglycaemia after meals
d. Reduced insulin demand
e. Permanent remission of diabetes
Answer: b. Increased risk of obesity and type 2 diabetes
Explanation: High-GI foods produce rapid post-prandial glucose rises and increased insulin demand. Diets rich in high-GI foods are associated with obesity and a higher risk of type 2 diabetes.
Summary for quick exam revision
The glycaemic index measures the ability of a food to raise blood glucose compared with glucose, which has a GI of 100. High-GI foods usually have a GI of 70 or above and cause rapid post-prandial hyperglycaemia. White bread is a classic high-GI food, with a GI around 80, and is therefore the correct answer in this question. White rice and baked potato are also high-GI examples. Brown rice is medium GI and is generally preferable to white rice for glycaemic control. Boiled new potatoes are medium GI, whereas baked potatoes are high GI, showing that cooking method matters. Digestive biscuits may sound sugary but are usually medium GI, making them an exam trap. Peanuts are low GI because they contain little carbohydrate, although they are calorie-dense. GI is not the same as sweetness, sugar content, or calorie content. A non-sweet refined starch, such as white bread, can have a higher GI than a sweet-tasting food. GI is affected by carbohydrate type, processing, cooking method, fibre content, fat and protein content, and fruit ripeness. High-GI diets can worsen post-meal glucose spikes and are associated with obesity and increased risk of type 2 diabetes. For exams, remember: white bread, white rice, and baked potato are high GI; brown rice, boiled new potato, porridge, couscous, and digestive biscuits are medium GI; peanuts and many fruit/vegetables are low GI.