Sugar and the Brain: C1 Reading and Vocabulary Unit

Level: C1

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Reading

Few foods carry as many beliefs about the mind as sugar does. Some people insist that a sweet snack sharpens concentration before an exam. Others warn that sugar is a drug that quietly damages memory and mood. Both views contain a grain of truth, and neither survives close inspection. The brain makes up about two percent of body weight but uses roughly a fifth of the body’s energy at rest, and its main fuel is glucose. That fact is real, yet it does not show whether extra sugar helps or harms. The evidence comes from very different kinds of study.

The best-known belief is the sugar rush, and it has been hard to dispel. In 1995, Mark Wolraich and colleagues combined 23 controlled experiments in a meta-analysis, a study that pools the results of earlier studies. Compared with a placebo, an inactive substitute, sugar did not change children’s behavior or thinking. A 1994 experiment by Daniel Hoover and Richard Milich suggests why the belief survives. Thirty-five boys received a sweetener without sugar, but half of their mothers were told that their sons had had a large dose. Those mothers rated their sons as more hyperactive. It was the expectation, not the sugar, that changed what they saw. Adults do not seem to gain either. A 2019 meta-analysis of 31 studies and 1,259 participants, led by Konstantinos Mantantzis, found no mood improvement at any point after carbohydrates were eaten, and found more fatigue and less alertness within the first hour.

The picture is mixed. A 2023 systematic review of 77 human studies reported that glucose can produce a transient improvement in some memory tasks, such as immediate recall. Over longer periods the results point the other way. In that review, all three cohort studies, which follow the same people over time, and eight of nine cross-sectional studies, which measure people once, linked added sugar to a higher risk of cognitive impairment.

Two large studies show both the appeal and the weakness of this kind of evidence. In the Framingham Heart Study, about 4,300 adults took memory tests and about 3,800 had brain scans. People who drank more sugary beverages had smaller total brain volume and poorer episodic memory, and daily fruit juice drinkers had a smaller hippocampus, a region important for learning. The authors used drinks as a proxy for total sugar intake, and what a single snapshot cannot show is which came first. In Britain’s Whitehall II study, men in the highest third of sugar intake from sweet food and drinks had 23 percent higher odds of a new common mental disorder five years later. The researchers tested for reverse causation, in which low mood leads to eating more sugar, and found no sign of it. No such link appeared in women, and the association in men was modest.

Experiments test cause more directly. In a 2020 randomized study, 110 healthy, lean adults ate either their usual diet or a Western-style diet, high in added sugar and saturated fat, for one week. The second group scored lower on a memory test linked to the hippocampus, although the difference had disappeared at a three-week follow-up. What the trial cannot separate is the effect of sugar from the effect of fat. In a 2026 review of 27 rodent studies, whose senior author works in Sydney, memory recovered after a switch back to a healthy diet when the earlier diet was high in fat, but not when it contained sugar. Scientists cannot extrapolate from rodents to people with confidence, and the reviewers called the persistent impairment after sugar a tentative conclusion.

The most heated argument concerns addiction. In rat experiments, animals given sugar solution for part of each day showed bingeing, signs of withdrawal, and repeated dopamine release in a reward area called the nucleus accumbens. A 2016 review by Margaret Westwater, Paul Fletcher, and Hisham Ziauddeen found little evidence for sugar addiction in humans. They argued that such behavior arises from intermittent access to palatable, or pleasant-tasting, food rather than from the chemistry of sugar. Other researchers disagree, and the question remains contested. It may be the pattern of access, not the sugar itself, that matters. Craving is real; the label is what researchers dispute.

Official guidance was written with other outcomes in mind. The World Health Organization’s 2015 guideline recommends that free sugars supply less than 10 percent of energy intake and, conditionally, under 5 percent. Those figures rest on evidence about body weight and tooth decay, not the brain, and they exclude sugars in fresh fruit. In people, one week of a diet rich in sugar and fat was followed by recovery within three weeks. In rodents, recovery after sugar-containing diets was incomplete. Which pattern applies to people who eat high-sugar diets for years has not been tested.

Vocabulary

Each word has a frequency score, a rank, and a tag. The score shows how common the word is in modern English: higher means more common, and each full point means roughly ten times more common. The rank is the word’s position on a list of about 321,000 English word forms, from most to least common. The tag shows where you are most likely to meet the word: Current, Formal, Literary, or Dated. The paragraph number shows where the word first appears in the reading. The labels are information, not instructions. Deciding which words are worth your time is up to you. How to read the scores, ranks, and tags.

The belief in a sugar rush has been hard to dispel.
The manager tried to dispel rumors that the office would close.

A 1995 meta-analysis combined 23 experiments on sugar and children’s behavior.
Before choosing a treatment, the doctor read a meta-analysis of twenty trials.

In many of the experiments, the placebo was a sweetener without sugar.
Half of the volunteers received the new pill, and half received a placebo.

The 2019 meta-analysis found more fatigue in the first hour after carbohydrates.
After a week of night shifts, the nurse felt a deep fatigue.

Glucose can produce a transient improvement in immediate recall.
The pain was transient and disappeared within an hour.

All three cohort studies linked added sugar to a higher risk of impairment.
The university tracked each cohort of first-year students for four years.

Daily fruit juice drinkers had a smaller hippocampus in the Framingham data.
Taxi drivers who memorize a city’s streets may develop a larger hippocampus.

The authors used sugary drinks as a proxy for total sugar intake.
Household income is sometimes used as a proxy for social class.

The Whitehall II team tested for reverse causation, in which low mood leads to more sugar.
Do unhappy people watch more television, or does television make them unhappy? That is a question of reverse causation.

The association in men was modest.
The company reported a modest increase in profits this year.

Scientists cannot extrapolate from rodents to people with confidence.
It is risky to extrapolate from one small town to the whole country.

The reviewers called the persistent impairment after sugar a tentative conclusion.
She had a persistent cough that lasted for months.

Rats with intermittent access to sugar showed bingeing behavior.
The village had only intermittent electricity during the storm.

The reviewers linked the behavior to palatable food rather than to sugar itself.
Adding a little lemon made the medicine more palatable.

Whether sugar is addictive remains contested.
The result of the election was contested in court.

Activity Page

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Speed Challenge

Answer 12 questions against the clock. Every wrong answer adds 5 seconds, and the lowest score wins. Open the speed challenge in a new tab.

Comprehension Questions

According to the reading, what is the main fuel of the brain, and why does the writer say this fact does not settle the question about extra sugar?
What did the 1995 meta-analysis by Wolraich and colleagues compare, and what did it find?
How did the Hoover and Milich experiment test the idea that expectation, not sugar, changes what parents see?
What did the 2019 meta-analysis find about adults, and what does the writer say is still unexplained?
How do the short-term and long-term findings in the 2023 systematic review differ?
What is the difference between a cohort study and a cross-sectional study, and why does the writer say a single snapshot is a weakness?
Why did the Whitehall II researchers test for reverse causation, and what did they conclude?
Why can the one-week Western-style diet trial not tell us that sugar alone affected memory, and what happened at the follow-up?
The writer places the rodent review and the human trial side by side at the end. What do the two results suggest, and why can they not yet be combined into one conclusion?

IELTS-Style Questions

True, False, or Not Given: “The Framingham Heart Study proved that sugary drinks shrink the hippocampus.” Explain your answer using evidence from the reading.
Yes, No, or Not Given: “The writer believes that sugar is completely harmless to the brain.” Explain your answer using evidence from the reading.
Author’s purpose: Why does the writer end with the sentence “Which pattern applies to people who eat high-sugar diets for years has not been tested”? Is its purpose to warn readers about sugar, to show what remains unknown, or something else?

AI Discussion Prompt

I just read an article about the effect of sugar on the brain. It covered the belief in a “sugar rush” and the experiments that tested it, a meta-analysis of sugar and mood in adults, short-term and long-term findings on memory, observational studies from the Framingham Heart Study and Whitehall II, a one-week diet trial and a review of rodent studies, the debate about sugar addiction, and the World Health Organization’s guideline on free sugars. I am an English learner at about C1 level. Please ask me one question at a time, starting with what I believed about sugar and concentration before I read the article. Respond to my ideas first, then briefly correct any language errors, and challenge my assumptions when it is useful.

AI Vocabulary Prompt

I want to practice vocabulary from an article about the effect of sugar on the brain. Please quiz me on the following words one at a time, using a mix of question types: multiple choice, true/false, and sentence completion. Give me feedback after each answer before moving on, and bring back the words I miss later. Here are the words: dispel, meta-analysis, placebo, fatigue, transient, cohort, hippocampus, proxy, reverse causation, modest, extrapolate, persistent, intermittent, palatable, contested.

Discussion Questions

Do you believe in the “sugar rush”? Where did you first hear about it, and has this article changed your view?
Think of a snack or drink you often choose when you need to concentrate. What do you expect it to do for you, and how do you know?
In the Hoover and Milich experiment, the mothers’ expectations changed what they saw. Can you think of a time when your own expectations changed how you judged a situation?
In your country, are sweet foods linked to rewards, celebrations, or comfort? How might those customs shape people’s beliefs about sugar?
The reading says the brain uses about a fifth of the body’s energy at rest. Does that surprise you? Why might a fact like this be used to support very different arguments?
When you read a health headline, how do you decide whether to trust it? What would you check first?
The Framingham and Whitehall II studies found associations, not proof of cause. Why do headlines often treat an association as a cause, and who is responsible for correcting this?
The 2020 diet trial combined added sugar with saturated fat. Is it fair to say anything about sugar alone from that study? Explain your view.
Researchers use rodents because they can control what animals eat. What are the advantages and the risks of learning about human health this way?
The reading says the idea of sugar addiction is contested. Do you think the word “addiction” is useful for describing strong cravings, or does it cause confusion?
Some countries tax sugary drinks, and many require labels on food. Should governments act on evidence that is still uncertain, or should they wait for firmer proof? Give reasons.
If a food company paid for a study on sugar and memory, how much would you trust its result? Would your answer change if the result was unfavorable to the company?
The WHO guideline rests on evidence about weight and tooth decay, not the brain. Should a guideline be judged only by the outcomes it was written for? Why or why not?
Scientists often say that more research is needed. When is that phrase an honest description of the evidence, and when might it be a way to avoid a conclusion?

Language Focus: Cleft Sentences for Emphasis

What it is: A cleft sentence splits one idea into two parts so that one part receives extra emphasis. Common patterns are It is/was + focus + that … and What + clause + is/was + focus.

Why writers use it: Cleft sentences help writers correct a common belief, show a contrast, or point to the key limitation of a study. They appear often in academic writing and in formal speaking.

Examples from the reading:

“It was the expectation, not the sugar, that changed what they saw.”
“…and what a single snapshot cannot show is which came first.”
“What the trial cannot separate is the effect of sugar from the effect of fat.”
“It may be the pattern of access, not the sugar itself, that matters.”

Practice task: Rewrite this sentence as a cleft sentence that emphasizes the size of the study: “The size of the study limits the conclusion.”

(Example answer: “What limits the conclusion is the size of the study. Also correct: It is the size of the study that limits the conclusion.”)

Recommended Resources

How Sugar Affects the Brain (TED-Ed, Nicole Avena). A five-minute animated video that presents one side of the addiction debate in paragraph 6: that sugar can overactivate the brain’s reward system.
No Such Thing as a Sugar Rush (University of Warwick). The university’s press release on the 2019 meta-analysis of carbohydrates and mood described in paragraph 2.
High Sugar Intake Linked with Poorer Long-Term Mental Health (University College London). A summary of the Whitehall II study in paragraph 4, including the test for reverse causation.
The Impact of Free and Added Sugars on Cognitive Function (Nutrients, PubMed abstract). The abstract of the 2023 systematic review of 77 studies described in paragraph 3.
Some Damage from High-Sugar Diets May Be Irreversible (Medical News Today, May 2026). A news report on the 2026 rodent review in paragraph 5, with comments from the senior author. The headline is stronger than the reviewers’ own wording.