Water-rich food fills you up on fewer calories, and in one key test water helped only when it was inside the food#
Volume eating means building meals around foods that are large and heavy for their calories, so you can eat a satisfying amount while taking in less energy. The idea rests on a solid finding from decades of feeding studies: over a meal or two, people tend to eat a fairly consistent amount of food, so lowering the calories per gram lowers the calories eaten, often without people feeling hungrier.
The most interesting part of that research is also the least known. In a classic experiment, a glass of water served alongside a food did not significantly reduce later intake, while the same water cooked into a soup cut intake at the next meal by about a quarter. This article covers why that happens, which foods it points to, the numbers behind simple swaps, and where volume eating stops working.
The experiment that separated water in food from water with food#
In 1999, researchers at Penn State gave 24 lean women one of three first courses on separate days, 17 minutes before an all-you-want lunch, plus a fourth day with no first course. Each first course supplied 1,128 kJ (about 270 kcal) from the same ingredients. What changed was where the water went1:
| First course (same calories) | Lunch intake afterward, excluding the first course |
|---|---|
| Chicken rice casserole | 1,639 kJ (≈392 kcal) |
| Same casserole plus a 356 g glass of water | 1,657 kJ (≈396 kcal) |
| Same ingredients made into a soup with that water | 1,209 kJ (≈289 kcal) |
(The kcal figures are our conversions from the paper's kilojoules.)
The soup reduced lunch intake by roughly 100 kcal compared with either casserole condition, raised fullness and reduced hunger. In this experiment, the same water served alongside the casserole did not affect satiety. And the women did not make up for the smaller lunch at dinner.
A later study with 60 men and women extended the finding. A vegetable soup served before lunch reduced total meal energy (soup plus lunch) by 20%, or about 134 kcal, compared with no soup. All four soup forms tested — broth and vegetables separately, chunky, part-pureed or fully pureed — reduced total meal intake, with no significant difference between them2.
The same lab's first-course salad studies showed the same direction with a twist: a large, low-energy-dense salad reduced the meal, while a salad made rich with dressing and cheese increased it. That study is unpacked in detail in estimating salad calories, because it doubles as a lesson in how one word can hide very different plates.
Energy density: the number behind volume eating#
Energy density is simply calories per gram. The concept is explained from an estimation angle in calorie density; here the point is what it means for fullness. The largest influence on the energy density of everyday foods is water, which adds weight and volume at 0 kcal/g, while fat adds about 9 kcal/g3.
That review groups foods into four bands, from "very low" (under 0.6 kcal/g) to "high" (4.0 to 9.0 kcal/g); the full band table, with the foods in each, lives in the calorie density article linked above. For volume eating, the band that matters most is the bottom one, which the review describes as mostly fruit, non-starchy vegetables and broth-based soups — though energy density depends on the specific food and how it is prepared, and some fruits sit higher. That is the part of the plate you can grow without the calories growing much with it, and it is the reason the soup and salad studies worked at all. Lean proteins, legumes and whole grains complement those foods on a volume plate, in measured portions.
Swaps with numbers#
The arithmetic below uses round values within those bands, not measurements of specific foods, and is ours rather than the studies'. It shows why the approach works on paper.
- Same weight, different band. A 300 g plate at 0.5 kcal/g is 150 kcal. The same 300 g at 2.0 kcal/g is 600 kcal. That fourfold gap is the whole idea.
- Half and half. Replace half of a 400 g pasta dish at about 1.5 kcal/g (600 kcal) with vegetables at about 0.4 kcal/g. The plate still weighs 400 g, but now carries about 380 kcal.
- Soup first. A broth-based vegetable soup before a meal reduced total meal intake by about 134 kcal in the soup study above — including the soup's own calories.
- Swap, don't just add. Replacing some of the richer ingredients with water-rich vegetables lowers a meal's calories while keeping its weight similar (simply adding vegetables lowers calories per gram but raises the total); adding oil, cheese or creamy dressing raises it fast, because each gram of fat carries as many calories as at least 15 g of very-low-density food (9 ÷ 0.6, our arithmetic).
Fiber-rich plants add to the effect because they tend to be bulky and water-rich at the same time; the case for fiber in its own right is in fiber benefits and targets.
Does it work for weight loss beyond a single meal?#
Single-meal studies are one thing; months are another. The evidence here is positive but smaller than the lab effects might suggest.
- A year-long trial. In a randomized trial of 97 women with obesity (71 completed), the group advised to reduce fat and increase water-rich foods lost about 1.5 kg more than the reduced-fat group, while eating a greater weight of food and reporting less hunger4. Why that matters for eating without counting is covered in losing weight without counting calories.
- A pooled analysis. A review of 13 experimental and observational studies (3,628 adults with obesity) linked lower energy density with lower body weight, but large differences between studies and inconsistent effect-size reporting limit interpretation5.
Those results are modest. Volume eating is better understood as a way to make a calorie deficit easier to live with than as a way to create a large one on its own.
Where volume eating stops working#
A light start doesn't cancel a heavy finish. The 2017 review is explicit: if a low-energy-dense salad is followed by large portions of high-energy-dense, palatable food, people are still at risk of overeating3. The first course helps only if the rest of the meal doesn't expand to fill the gap.
Water with a meal is not the same as water in it. In the 1999 study, water served alongside food did not reduce intake, while the same water in soup did. Water drunk before meals is a separate question this study did not test.
Taste has to survive the swap. The review stresses that lowering energy density only helps if the food stays acceptable. A plate that is technically low-density but unpleasant to eat tends not to last as a habit.
Protein doesn't come with the volume. Very-low-density foods are mostly fruit and non-starchy vegetables, which carry little protein. A plate built only for volume can leave protein short, which matters both for fullness and for keeping muscle while losing weight. The role protein plays in fullness is covered in protein and satiety.
The long-term evidence is thin. The same review calls for research on the long-term effects of lowering energy density in people's everyday environments. Most of the strong data are from single meals or a few days in a laboratory.
FAQ#
What is volume eating?#
Volume eating means choosing foods with few calories per gram — many fresh fruits, non-starchy vegetables and broth-based soups — so a satisfying amount of food carries fewer calories.
Does drinking water with a meal work like eating soup?#
Not in the key experiment. A glass of water served with a food did not reduce later intake, while the same water cooked into soup cut the next meal by roughly 100 kcal. Water before meals was not tested there.
How much weight can volume eating help you lose?#
A year-long trial in women with obesity found about 1.5 kg more loss than a low-fat approach alone; pooled evidence points the same way but is too inconsistent to give a reliable average.
Which foods are best for volume eating?#
Many fresh fruits, non-starchy vegetables and broth-based soups, which are mostly water. Lean proteins and legumes round out a filling plate.
Sources#
- Rolls BJ, Bell EA, Thorwart ML. Water incorporated into a food but not served with a food decreases energy intake in lean women. American Journal of Clinical Nutrition. 1999;70(4):448-455.
- Flood JE, Rolls BJ. Soup preloads in a variety of forms reduce meal energy intake. Appetite. 2007;49(3):626-634.
- Rolls BJ. Dietary energy density: Applying behavioural science to weight management. Nutrition Bulletin. 2017;42(3):246-253.
- Ello-Martin JA, Roe LS, Ledikwe JH, Beach AM, Rolls BJ. Dietary energy density in the treatment of obesity: a year-long trial comparing 2 weight-loss diets. American Journal of Clinical Nutrition. 2007;85(6):1465-1477.
- Stelmach-Mardas M, Rodacki T, Dobrowolska-Iwanek J, et al. Link between Food Energy Density and Body Weight Changes in Obese Adults. Nutrients. 2016;8(4):229.
Source: BurnWeek — "Volume eating: how to eat more food for fewer calories", https://burnweek.fit/blog/volume-eating-explained/. Licensed CC BY 4.0: free to quote or reuse with a link to this page.
