Longetic keeps every lab report you upload and shows each value next to that lab's own reference range, which is why this piece is about the one thing a result never prints: what went into you before the blood was drawn. An orange and a glass of orange juice are not the same input, the published numbers say so, and England and Spain say so in very different words.
Do whole fruit and fruit juice raise blood sugar the same way?
Longetic does not track food or drink, so take this as published evidence rather than a reading of your own diet. On the glucose scale, the 2008 international tables put raw apple at 36 and apple juice at 41, raw orange at 43 and orange juice at 50, so juice sits higher in each pair. Both members of each pair still land inside the low band, so the gap is real and it is modest.
The glycemic index ranks a carbohydrate food by how far it raises blood glucose against a reference food, with pure glucose set at 100. The International Tables of Glycemic Index and Glycemic Load Values were published in Diabetes Care in December 2008 and carry over 2,480 individual food items in an online-only appendix. The four numbers below come from the summary table printed in the article itself, which its own caption describes as "The average GI of 62 common foods derived from multiple studies by different laboratories".
That caption matters, because it means none of these figures is a single measurement of a single apple.
| Food | GI as the 2008 table prints it | What the table says about the figure |
|---|---|---|
| Apple, raw | 36 ± 2 | Average of all available data |
| Apple juice | 41 ± 2 | No footnote mark on this row |
| Orange, raw | 43 ± 3 | Average of all available data |
| Orange juice | 50 ± 2 | No footnote mark on this row |
| Glucose, the reference food | 103 ± 3 | Scale anchor, printed in the same column |
Two things in that table need saying out loud. The paper prints no scale label on it, so it is glucose-referenced by its own anchors, glucose at 103 ± 3 and white wheat bread at 75 ± 2 in the same column, and by the authors' own line that "To avoid confusion, the glucose scale is recommended for final reporting." And the two raw-fruit rows carry a footnote reading "Average of all available data" which the two juice rows do not.
What the glycemic index numbers actually say
Both sides of each pair land in the low band. The Linus Pauling Institute at Oregon State University sets low glycemic index at 55 or under on the glucose scale, intermediate at 56 to 69 and high at 70 or above. Apple at 36 and apple juice at 41 are both low by that definition, so on this measure alone juice is higher than the fruit it came from and still not a high-glycemic food.
Glycemic load is the second number, and it brings portion size into the picture. The same Linus Pauling Institute page sets a low glycemic load at 10 or under for a typical serving, intermediate at 11 to 19 and high at 20 or above, and lists one medium raw apple at 15 g of carbohydrate with a glycemic load of 6.
That page is also where two respectable sources stop agreeing, and the disagreement is worth printing rather than smoothing over. The Linus Pauling Institute gives raw apple a glycemic index of 39; the 2008 Diabetes Care table gives 36 ± 2. The glycemic load of 6 is computed from the institute's own 39, not from the 36. The page carries no "last updated" line at all; what it carries is "Updated in March 2016 by: Barbara Delage, Ph.D." and a review in the same month. Anyone who compares a figure they read somewhere against a figure on their own plate is already two sources deep in exactly this kind of mismatch.
Why juicing changes the sugar, and what each country calls it
Crushing or blending fruit releases the sugars held inside its structure. England names the result free sugars and treats juice differently from fruit because of it, and the World Health Organization uses the same category and keeps the sugars in fresh fruit out of it. Spain's national food safety agency arrives at the same conclusion by a different route, and without attaching a number to it.
The NHS 5 A Day page, last reviewed on 9 June 2026, puts the mechanism plainly: "Crushing fruit and vegetables into juice and smoothies releases the sugars they contain, which can damage teeth." The same page then gives advice that is often repeated for the wrong reason: "Juices and smoothies should be consumed at mealtimes, not as a between-meal snack, to reduce the risk of tooth decay." The reason the NHS gives for the mealtime advice is that one, not blood sugar.
The free sugars framing lives on a different NHS page, Sugar: the facts, last reviewed on 19 May 2023 with a next review date of 19 May 2026 that has already passed. It lists among free sugars "and unsweetened fruit juices, vegetable juices and smoothies", then draws the line: "Sugar found naturally in milk, fruit and vegetables does not count as free sugars." The very next sentence carries the condition that makes the first one true: "But sugar in fruit is not considered free sugars unless the fruit is juiced or puréed."
The World Health Organization set the same boundary in a news release dated 4 March 2015, which accompanies its guideline rather than being it. Its definition of free sugars covers added sugars and "and sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates". Its exclusion of fresh fruit, vegetables and milk comes with its own stated reason, and the reason is an absence rather than a finding: "because there is no reported evidence of adverse effects of consuming these sugars". WHO's own wording is "fresh fruits and vegetables", not whole fruit.
Spain's national statement comes from the Comité Científico of the Agencia Española de Seguridad Alimentaria y Nutrición, in report AESAN-2022-007, approved in plenary session on 27 July 2022. The report makes the point twice, once as a conclusion and once inside the recommendation itself: "considerando que el consumo de zumos de frutas no es un sustituto de la fruta entera." Neither sentence is hedged, and neither carries a figure.
Does juice count as a portion of fruit in England and in Spain?
England gives a number and Spain gives a principle. In England, unsweetened juice and smoothies count once towards 5 A Day however much you drink, and the combined daily total is 150ml, while Spain's national agency says juice is not a substitute for whole fruit and prints no millilitre figure anywhere. The same split runs through the units your results come back in.
| What differs | England | Spain |
|---|---|---|
| Does juice count as a portion of fruit | Once a day at most, however much you drink | Not a substitute for whole fruit |
| Daily limit in millilitres | 150ml of juice and smoothies combined | Not defined nationally |
| Who states it | NHS, 5 A Day pages | AESAN scientific committee, report 2022-007 |
| Reason the source gives | Juicing releases the sugars | Juice sugars count as free sugars |
| Unit a glucose result is printed in | mmol/L | mg/dL |
| Unit an HbA1c result is printed in | mmol/mol, with % in brackets | % |
The once-a-day cap is spelled out on the NHS 5 A Day portion sizes page, with an example rather than a rule: "For example, if you have 2 glasses of fruit juice and a smoothie in 1 day, that still only counts as 1 portion." That page was last reviewed on 19 July 2022 against a next review due on 19 July 2025, so it is more than a year past its own date. NHS inform in Scotland carries the same rule on a page last updated 14 October 2026, in words of its own: "counts as a maximum of one portion a day regardless of how many portions you have".
Below the national level, Spanish regional health services do give figures, and they do not match each other or England. The Comunidad de Madrid's healthy eating page, last updated on 27 May 2026, says "No es recomendable consumir más de un vaso pequeño de zumo de fruta natural al día.", which names a small glass without attaching millilitres to it. The Galician health service, on a page dated 2 February 2023 and written for parents, is blunter: "No se puede considerar una ración de zumo de frutas equivalente a una ración de fruta," and closes with its qualifier intact: "En definitiva, el consumo de zumos, aunque sean naturales, no deben desplazar al consumo de fruta entera."
What the trial and the cohorts actually found
Two studies are usually cited here and both are usually cited wrong. A crossover trial found that a whole apple before lunch cut intake for the whole eating occasion by 15% against no preload at all, not against juice. A cohort analysis found a 7% lower risk when three weekly servings of juice were replaced by whole fruit, and that is a substitution estimate from observational data.
Flood-Obbagy and Rolls published the trial in Appetite in 2009. Fifty-eight adults, once a week for five weeks, took one of four preloads matched at 266 g and 125 kcal, or no preload at all, then ate a test meal freely fifteen minutes later. The reported result was that "Results showed that eating apple reduced lunch energy intake (preload + test meal) by 15% (187 ± 36 kcal [782 ± 151 kJ])", and the comparison inside that sentence is "compared to control (p < 0.0001)". The apple-against-juice comparison is stated separately and without a figure attached: whole apple "decreased energy intake compared to applesauce and both juices." Fullness ratings ran "apple > applesauce > both juices > control".
Muraki and colleagues published the cohort analysis in The BMJ on 29 August 2013, pooling 66 105 women in the Nurses' Health Study, 85 104 women in Nurses' Health Study II and 36 173 men in the Health Professionals Follow-up Study, with 12 198 cases of type 2 diabetes across 3 464 641 person years. For replacing three servings a week of fruit juice with the same amount of whole fruit, the paper reports that risk "was 7% (95% confidence interval 4% to 9%) lower". That is an association observed in cohorts, not a measured effect of making the swap.
The 7% is the figure for whole fruit in general, and it is the weakest number in the paper's own list. The same substitution against individual fruits gives "33% (24% to 40%) lower for blueberries", "19% (14% to 24%) lower for grapes and raisins" and "14% (11% to 18%) lower for apples and pears". One fruit ran the other way: for greater cantaloupe consumption the pooled hazard ratio was "1.10 (1.02 to 1.18)". Reading the paper as a single sentence about fruit loses most of what it found.
Which blood sugar tests get ordered, and what each one measures
Two tests do most of the work and they ask different things of you. An HbA1c, called A1C in the United States, reports an average across a period of months and needs no fasting, while a fasting plasma glucose is a single point in time and does need fasting. Which unit the result is printed in depends on which country drew the blood, and so does how much you are told.
The National Institute of Diabetes and Digestive and Kidney Diseases, on a page last reviewed in July 2022, writes that "The A1C test is a blood test that provides your average levels of blood glucose over the last 3 months." and, of the same test, "You can eat and drink before this test." For the fasting plasma glucose it states a condition before it states a number: "For the most reliable results, your doctor will give you the test in the morning", and then "after you have fasted for at least 8 hours." Fasting there means "having nothing to eat or drink except sips of water".
England words it differently and in fewer places. None of the NHS pages read for this article uses the term HbA1c, and none gives an hour count; the NHS blood tests page says only that you may need to "not eat or drink anything other than water (fast)", inside a sentence already hedged with "for a short time before some tests". The HbA1c wording English readers actually meet comes from Diabetes UK, which says "HbA1c is your average blood glucose (sugar) levels for the last two to three months." That page prints no date of any kind. Two to three months and three months are two claims from two countries, and it is worth knowing which one you read.
Spain tells patients to fast in clock time rather than in hours. The semFYC patient guide says "Normalmente, el análisis de sangre debe hacerse en ayunas." and then, because the draw happens in the morning, "Como siempre se hacen por la mañana, piense que usted debe acabar de cenar alrededor de las nueve de la noche." The hour count in Spain lives in a document written for professionals, not patients, and that document does not agree with itself: a 2007 Ministry of Health laboratory guide prints "Ayuno: como norma general se recomienda un ayuno de 8 horas previo a la extracción." in one place and recommends eight to ten hours in another.
The units differ too, and this is the same mismatch that makes any number from one system unreadable in the other. In England, the NHS page on low blood sugar, itself past its next review date of 3 August 2026, prints glucose in mmol/L, and Diabetes UK gives an HbA1c in mmol/mol with the % figure in brackets, noting that mmol/mol "has been the standard measurement for glucose levels since 2009". Spanish patient material runs the other way: a semFYC patient guide prints glucose in mg/dL and HbA1c as a %. If you keep results from both countries, the reason two numbers refuse to line up is covered in why unit conversion matters in health care.
What to write down before a blood sugar test
Nothing in the official guidance asks you to record any of this, which is the gap worth filling yourself. Before a fasting test, note the time you last ate or drank anything other than water, and keep each result with its date, the laboratory that ran it, and that laboratory's own reference range exactly as printed. If your results come from two countries, keep the unit as printed as well.
This is a real absence rather than a gap in our reading. Of the pages checked for this article, none instructs a patient to write down what they ate or drank before a blood test, or the time of their last food or drink: the NHS blood tests page, the NHS type 2 diabetes pages, the Diabetes UK HbA1c page, the semFYC patient guide, a Ministry of Health laboratory document, a Comunidad de Madrid hospital patient instruction and a Galician health service page on blood draws. The instruction to fast is always there. The instruction to record anything is not.
One Spanish document makes the point better than any argument could. The same Ministry of Health laboratory guide that never asks a patient to note the time of their last meal does ask them to note a time, for a urine collection: "Antes de acostarse, orinar en el WC y anotar la hora exacta en el recipiente." The habit exists in official material. It has simply never been pointed at food and drink.
Context before a draw is not only about food, which is why a hard workout before a blood test is worth noting in the same line, and why the markers a fasting protocol actually moves are a separate question from this one, covered in track health markers while fasting. If you want the wider list of records worth keeping, it sits alongside the other items in 11 health essentials for a long life.
We publish this and we sell an app, so the boundary belongs in the open. Longetic stores lab reports from any source and shows each value next to that laboratory's own reference range, which is the part that goes missing the moment a number is copied out of its report. It does not track food, drink, weight or activity of any kind, it does not convert units, and it does not decide what a result means. What goes in is what you upload or type, which for a fasting test is one line: the date, the time of the draw, and when you last ate. Everything else belongs in a conversation with the clinician who ordered the test, along with everything you already take. Nothing here is advice about what to eat or how to be treated.
