The Ultimate Volumetrics Diet: Smart, Simple, Science-Based Strategies for Losing Weight and Keeping It Off

Overall score

Scientific accuracy

Reference accuracy

Healthfulness

How hard would it be to apply the book's advice? Fairly easy

Book published in 2013

Published by William Morrow Cookbooks

Illustrated Edition, Paperback

Review posted March 18, 2022

Primary reviewer: Shaun Ward

Peer reviewer: Stephan Guyenet

Table of contents

1. Introduction
2. Scientific accuracy
3. Reference accuracy
4. Healthfulness
5. Most unusual claim
6. Other
7. Conclusion
8. Updates

Claim 1

Reducing the energy density of the diet promotes weight loss.

Supporting quote(s) and page number(s)

[Page 16] “Then you will love Volumetrics, a positive, scientifically proven approach to weight management that focuses on what you can eat.”

[Page 19] “You will find that as you eat more of the lower-[calorie density] foods and less of those higher in CD, your daily calorie intake will go down and you will feel full and satisfied.”

[Page 21] TITLE: “Why Low Calorie Density Equals Lower Calorie Intake.”

[Page 21] “But when you are deciding how much to eat at a meal, you will be guided more by how much you think you should eat than by your biology.”

[Page 22] “Here is another benefit to eating the Volumetrics way: several trials show that it can help you lose weight.”

[Page 23] “Over a day, people generally eat a similar amount of food by weight. Choosing foods with a lower [calorie density] will allow you to eat your usual amount of food while reducing your calorie intake.”

[Page 30] “In one of our studies, people who decreased the [calorie density] of their daily diet by just 0.5 calories per gram ate two-thirds of a pound more food, cut out 500 calories per day, and lost weight!”

Criterion 1.1. How well is the claim supported by current evidence?

4 out of 4

The claim that reducing the energy density of the diet promotes weight loss received a score of 4, meaning it is strongly supported by scientific evidence.

Short-term interventional trials consistently support the claim that low energy density diets promote weight loss. A meta-analysis of 9 randomized controlled trials lasting from 8 weeks to 9 months, all of which measured food energy density and body weight changes in obese adults, found a statistically significant association between low energy density foods and body weight reduction. The magnitude of body weight reduction was small (-0.48kg) but we note that the dietary interventions didn’t target large changes in energy density per se; rather, energy density indirectly changed from targeted reductions in dietary fat or sugar intake. To what degree energy density and macronutrient changes can be reliably separated as independent variables has not been clarified in the literature; however, an earlier review of several short-term intervention studies suggested that dietary fat reduction only reduces energy intake to the extent that it reduces the energy density of the diet. Thus, while there are nuances in the relationship between energy density and body weight, the overall evidence confirms that energy density impacts body weight.

Some individual studies can also be used to support the notion that a larger reduction of energy density causes greater weight loss. For example, when participants completed one of two 14-week weight loss programs (in free-living conditions) and were assessed for energy density changes, the change in participants’ energy density during the intervention was significantly associated with their percent change in body weight post-intervention.

The results of long-term intervention trials are more mixed than short-term intervention trials. The two most cited papers supporting a long-term weight loss benefit when reducing the energy density of the diet happen to come from the research group of the primary Volumetrics author, Barbara Rolls.

The first of these studies was a 12-month clinical trial that found incorporating two daily servings of low energy density soup led to greater weight loss after 6 months of targeted weight loss and a further 6 months of weight maintenance, compared to the inclusion of high energy density snack foods containing the same number of calories. The researchers reported that the difference in energy density between snacks was the critical factor for differences in daily energy intake since the study foods had similar energy content yet differed in energy density. Interestingly, however, the comparison group—advised only to follow a reduced-calorie diet without intervention snacks—actually achieved similar weight loss to the reduced-energy-density groups despite reporting a greater dietary energy density. This again implies that dietary energy density isn’t the only determinant of energy intake, and reducing energy density isn’t necessarily superior to other weight loss approaches.

The second study from Barbara Rolls’ research group reported similar weight loss benefits for reducing energy density. In a 12-month trial in women with obesity, advice to decrease the energy density of the diet by adding water-rich foods (increasing fruit and vegetable consumption) and reducing dietary fat intake led to significantly more weight loss after 6 months than advice to reduce dietary fat intake alone. No significant differences between groups were found after 12 months of intervention, although the lower-energy-density group tended toward greater weight loss. Both groups reduced dietary energy density and lost a significant amount of weight after 1 year compared to their baseline values, but as is typical of most weight loss trials, they also marginally increased (0.3-1.0 kg) body weight from months 6 to 12 despite dietary energy density remaining essentially unchanged and BMI remaining ‘obese’.

This particular trial was also used to represent the Volumetrics diet in a network meta-analysis that assessed differences in weight loss from named diet programs after 6 months of intervention; Volumetrics was directly compared to low-fat, low-carbohydrate, and moderate macronutrient dietary approaches. The energy density of other dietary approaches was not reported, although it’s assumed they differed substantially from Volumetrics based on the types of foods they include. If this assumption is correct, the results are interesting because among the diets with ‘high’ or ‘moderate’ certainty evidence, Volumetrics was listed as superior to the least effective diet interventions (The Biggest Loser, Slimming World) but inferior to the most effective popular named diets (Jenny Craig, Atkins). As the Atkins diet prioritizes the intake of energy dense foods such as high-fat meats, dairy, fish, and eggs, it’s an example of a diet that largely opposes the Volumetrics approach to weight loss but achieved superior weight loss results in the compared studies. This illustrates that weight loss depends on more than just the energy density of the diet.

Overall, a literature summary suggests that energy density is an important factor determining weight loss success, among other nutritional and behavioral factors. We only found one long-term randomized trial that offered evidence against any role of energy density as an important weight loss factor. Yet, unlike the prior studies discussed that recruited primarily overweight or obese participants, only a quarter of the cohort in this study were clinically obese at baseline. The study also used a non-random population sample (breast cancer survivors) that does not reflect the general population. As a result, this study does not provide strong evidence against energy density promoting weight loss in the average person who wants to lose weight.

The evidence from interventional research for a weight loss benefit by reducing dietary energy density is generally positive, particularly up to 6 months and for individuals that are overweight or obese. Evidence for a benefit at 12 months or beyond is less strong, but this isn’t surprising given the waning effectiveness of all weight loss diets over time. In fact, a meta-analysis of 29 long-term weight loss maintenance studies (up to five years) demonstrated that just over half of all weight lost during intervention periods is regained by two years, and 80% by five years. Dietary adherence appears to be a major problem for long-term weight loss success. Yet even despite this, a systematic review of the determinants of long-term weight loss suggests that a high intake of fruit and vegetables (foods low in energy density) are positively predictive of weight loss maintenance. Whether this determinant is related directly to reducing dietary energy density or not is yet to be confirmed, but it’s very likely to be a contributing factor based on the totality of evidence.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

4 out of 4

The references cited in Volumetrics to support this claim received a score of 4, indicating that they offer evidence that is intrinsically convincing and predominantly supports the author’s claim. The primary studies used to support this claim were the two 12-month interventions from the research group of Barbara Rolls, which were both cited accurately and support a weight loss benefit to reducing the caloric density of the diet. We note that elements of these studies that did not support the authors’ claims as strongly were withheld, such as the control group comparisons and the lack of a sustained weight loss advantage beyond 6 months, but the studies still offered convincing evidence for the claim overall.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

4 out of 4

Volumetrics received a score of 4, indicating the strength of the claim that reducing the calorie density of the diet promotes weight loss accurately represents the size and uncertainty of the effect. The bulk of the scientific evidence supports that dietary energy density is an important factor contributing to weight loss success.

We note, however, that the book does not discuss the evidence or study details that offer arguments thought to oppose their position, including: the uncertainty regarding the long-term weight loss benefit; the multifactorial nature of body weight management; the weight loss benefits from low-carbohydrate, high-fat, energy dense diets; research comparing Volumetrics to contrasting approaches such as the Atkins diet.

Overall (average) score for claim 1

4.0 out of 4

Claim 2

Low energy density foods increase satiety and reduce energy intake.

Supporting quote(s) and page number(s)

[Page xv] “Research shows that lowering the [calorie density] of foods will help you to keep full while eating fewer calories.”

[Page xvii] “Volumetrics foods can be highly filling and satisfying.”

[Page 3] “You’ll be eating satisfying amounts that allow you to feel full and manage hunger while you’re losing weight”

[Page 19] “Foods with a high water content help fill you up since water bulks up food, giving you bigger portions without more calories.”

[Page 21] “They eat the same amount of the casserole each week [regardless of calorie density], with fewer calories when [calorie density] is lower—and don’t feel hungrier or compensate by eating more later.”

[Page 48] “Lots of studies from my lab show that a low-calorie, low caloric density appetizer helps you to manage the calories in your meal.”

Criterion 1.1. How well is the claim supported by current evidence?

4 out of 4

The claim that foods low in energy density increase satiety and reduce energy intake received a score of 4, meaning it is strongly supported by scientific evidence.

The most common method to assess food satiety values are preload studies. This involves participants consuming a specific type of food (the preload) prior to a test meal, like how an appetizer would be eaten. Some foods used as preloads reduce subsequent intake of the test meal more than others, and this is thought to reflect their satiety value. A meta-analysis of preload studies reported that the energy density of preloads did not significantly affect the energy intake of a subsequent test meal(s). Results differed greatly between studies, however, and a subgroup analysis found that in comparison to high energy density preloads, consuming low energy density preloads with higher water or fiber content significantly lowered subsequent energy intake. Additionally, total energy intake (preload plus test meal) was significantly lower when a lower energy density preload was compared to a higher energy density preload, regardless of whether preloads were matched by weight or energy content. This emphasizes that the type of preload and the type of comparison food are critical when determining satiety values. In this case, the most effective types of preloads for increasing fullness and reducing test meal energy consumption were soups and casseroles with a high water and fiber content, salads, diluted milk, and yogurt-based milkshakes with a high air content.

The main caveat to preload research on energy density is that a control group (that does not consume any preload) is often absent; low energy density preloads are typically compared only to higher energy density preloads. Not only this, but the studies that do happen to include a no-preload control group tend to find that low energy density preloads don’t reduce total energy intake (preload plus test meal) relative to the no-preload control, implying that low energy density preloads are no more effective than not eating a preload at all. One randomized controlled trial hypothesized that using a less palatable test meal will elucidate the satiety benefits of a low energy density preload versus a no-preload control group; however, a lack of differences in total energy intake between preload conditions was still apparent.  While the lowest total energy intakes in this study were those including preloads and test meals with the lowest energy density, the impact of the preload was small (< 100 kcal) and not statistically significant.

Nevertheless, while questions remain about the effectiveness of preloading meals with low energy density foods, the influence of energy density still appears to be an important factor contributing to the total amount of energy consumed at any single meal. A randomized controlled trial, previously mentioned, found that even when the presence of a preload has little effect on total energy intake, changing the energy density and portion size of the test meal independently affected the energy consumed at that meal. Another crossover study found similar results by incorporating more water into a casserole test meal, reporting a decreasing trend in the participant’s energy intake as the energy density of the test meal reduced. In other words, while low-energy-density “appetizers” may not reduce energy intake more than skipping the appetizer, reducing the energy density of the main meal does appear to reduce energy intake.

The satiety benefit of individual foods or meals appears to hold when comparing between types of carbohydrate-rich foods. In a randomized crossover study where different carbohydrate foods were served in portions containing equal carbohydrate and calories alongside meat and vegetables, participants felt significantly fuller, more satisfied, and wanted to eat less following a potato meal as compared with rice or pasta meals. The researchers stated that “The superior satiating effect of potato compared with rice and pasta in a mixed meal was consistent with its lower energy density.”

Similar benefits of potatoes over other starchy foods have been reported elsewhere, although the extent to which energy density contributes to these differences among other factors (such as nutrient content or palatability) has not been explored in great depth. One study that measured participants’ beliefs about a food’s satiety value suggested that energy density may influence satiety expectations because our presumptions are more in line with the perceived volume of food rather than its energy content. Per unit energy, foods lower in energy density offer measurably and visually larger volumes of food.

We also note that the weight loss benefit for low energy density diets, as discussed in claim 1, can be used as further evidence that low energy density foods increase satiety and reduce total energy consumed at a meal. Due to the known relationship between satiety and weight loss, it can be reasonably assumed that the weight loss benefits of foods lower in energy density is partly as a function of increased satiety. Please refer to claim 1 for a more detailed breakdown of energy density and weight loss.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

3 out of 4

The references cited in Volumetrics to support this claim received a score of 3, indicating that they offer evidence that is intrinsically convincing and moderately supports the book’s claim. Most of the relevant references were controlled intervention studies and cited accurately, although too much emphasis was placed on preload studies from the research group of Barbara Rolls. It’s our view that the strongest evidence for the claim is found with studies that test caloric density as part of normal eating habits (i.e., as part of conventional meals) rather than as preloads before a meal. There was also a trend for Volumetrics to withhold elements of preload studies that did not support its claims as strongly, such as the lack of differences in total energy consumption when preload interventions were compared to no-preload control groups.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

4 out of 4

Volumetrics’ references received a score of 4, indicating the strength of the claim that foods low in energy density increase satiety and reduce energy intake accurately represents the size and uncertainty of the effect. Although much of the relevant literature pertains to preload studies that do not consistently report benefits for reducing total energy intake (preload plus test meal) compared to no-preload control groups, there is strong evidence from intervention studies that energy density is an important factor determining the amount of energy consumed at any single meal. When compared to high energy density foods, low energy density foods consistently reduce total energy intake and hunger per calorie, regardless of study type. The satiety benefit appears to be stronger when analyzing the cumulative effect over the course of a day(s), rather than acute effects of snacks or ‘preloads’ consumed in the lead-up to a single meal.

Overall (average) score for claim 2

3.7 out of 4

Claim 3

Reducing dietary fat is superior to reducing carbohydrate for weight loss.

Supporting quote(s) and page number(s)

[Page 72] On page 72, the book discusses the weight loss impact of low-carbohydrate diets higher in fat and protein. “High-protein diets come in and out of fashion. For some of us, the prospect of eating unlimited quantities of protein-rich, high-fat foods, such as cheese and steak, while shedding pounds is irresistible… What has surprised me and other weight-loss researchers is that these strict high-protein diets work and may even provide health benefits—at least for a short while… Dieters on such diets don’t learn sustainable eating habits that will keep the weight off, and high-protein diets have not been found to lead to long-term weight loss.”

[Page 87] “The majority of studies indicate that advising participants to reduce their fat intake promotes weight loss.”

[Page 89] “Replace high-fat foods with vegetables and fruits, legumes, and whole grains to bring down [calorie density] while giving you satisfying amounts of food.”

[Page 89] “Switch to lower-fat alternatives.”

Criterion 1.1. How well is the claim supported by current evidence?

2 out of 4

The claim that reducing dietary fat is superior to reducing dietary carbohydrate for weight loss is weakly supported by current evidence.

While many claims regarding uniquely fattening properties of both dietary fat and carbohydrates persist, no macronutrient has been convincingly shown to influence adiposity independent of daily energy intake. A meta-analysis of controlled isocaloric feeding studies supports this position. By analyzing studies that varied substantially in the proportions of dietary fat (4–84% of total energy) and carbohydrate (1–83% of total energy) that participants consumed during the intervention, the meta-analysis results indicated very little impact of macronutrient ratio on changes in body fat mass when total energy and protein intake were held constant. While a couple of re-analyses of the data have suggested the possibility that high-carbohydrate diets increase energy expenditure in short trials but high-fat diets increase energy expenditure in long trials, the effect size is small and the same analysis has not yet been performed for body fat.

It can be argued, however, that Volumetrics speaks mainly in the context of ad libitum food intake (eating without constraints) rather than controlled feeding conditions. In other words, even if no nutrient is fattening when calories are held constant, Volumetrics argues that dietary fat still promotes energy overconsumption more so than dietary carbohydrate due to its higher energy density. But as we stated in our response to claim 1, a network meta-analysis that assessed differences in weight loss after 6 of intervention reported that Volumetrics diet did not perform better than some high-fat dietary approaches (Atkins). Another finding in this same meta-analysis was that body weight changes were similar between 17 specific dietary patterns ranging considerably in dietary fat and carbohydrate intake after 6 and 12 months. It would appear, then, that there is no meaningful long-term difference in weight loss between low-fat and low-carb diets based on the bulk of the scientific literature.

Even if we look specifically at the longest randomized controlled trial that intervened with ad libitum low-carbohydrate and low-fat diets, the DIETFITS study, we can gather direct and robust evidence against claims that higher dietary fat intakes must be avoided due to calorie density concerns. DIETFITs took 609 “healthy” adults (without diabetes with a BMI between 28 – 40) and randomized them to an ad libitum healthy low-fat (~48-53% carbohydrate) or healthy low-carbohydrate (~23-30% carbohydrate) diet for 12 months, while protein intake remained similar (21 – 23% total energy intake). The results were that daily energy intake was not significantly different between diet groups at baseline or at any subsequent time point throughout the study (3, 6 and 12 months) despite the participants being given no instructions on food quantity. The mean reduction in energy intake in both diet groups, relative to baseline, was ~500 – 600 kcal per day. There were no significant differences in weight loss between groups.

Based on the totality of the evidence, successful dietary approaches include high dietary fat intakes. There is no clear evidence suggesting that preferentially lowering dietary fat instead of carbohydrate leads to superior weight loss. In fact, even the European Guidelines for Obesity Management in Adults now state that ketogenic diets, which comprise over 70% of total daily calories from dietary fat, “can be recommended as an effective dietary treatment for individuals with obesity after considering potential contra-indications and keeping in mind that any dietary treatment has to be personalized”.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

2 out of 4

The references cited in Volumetrics to support this claim received a score of 2, indicating that they offer weakly convincing evidence. The only reference that appeared to support the authors’ claim was a research synthesis suggesting that dietary fat should be moderated (up to 35% of total energy intake) due to palatability concerns. Yet upon closer inspection, the authors of this research review stated that “we believe that evidence is compelling that for people attempting to lose weight, low-fat diets remain a reasonably useful tool. However, this does not imply that they are necessarily more useful than other dietary manipulations for weight loss”.

The other relevant references in Volumetrics do not support the claim. A reference to a long-term randomized controlled trial that compared different macronutrient compositions was provided, but the results were not in favor of a lower dietary fat approach for greater weight loss. The conclusion of this study was that “Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.” Another reference in Volumetrics to a 2-year weight loss comparison between a low-fat and low-carbohydrate diet reported similar findings; there were no significant differences in body weight between the dietary groups at any time point over the 2-year period.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

2 out of 4

Volumetrics references received a score of 2, indicating the strength of the claim is moderately overstated. This score could have perhaps been lower, but we note that Volumetrics made brief mention that long-term evidence does not necessarily support the superiority of any one macronutrient ratio—even though this was in contradiction to many of the statements, recommendations, and recipes in the book that are almost all carbohydrate-dominant. For example, Volumetrics gives more leniency to whole grain products than it does for foods higher in dietary fat, stating to “include at least one whole grain at each meal” [Page 81] and to “snack on whole grains” [Page 81].

Overall (average) score for claim 3

2.0 out of 4

Overall (average) score for scientific accuracy

3.2 out of 4

Summary of the health-related intervention promoted in the book

The Ultimate Volumetrics Diet is a 12-week weight loss program that promotes a reduction in dietary energy density. Volumetrics proposes that dieters focus their meals on foods with lower energy density to feel fuller on fewer calories, more satisfied, and promote weight loss naturally. Emphasis is placed on building every meal on the least energy dense foods: fruits, vegetables, wholegrains, legumes, low-fat dairy, and lean meats and fish. A cautious approach to portion sizes is advised for energy dense foods: nuts, seeds, eggs, fatty meats and dairy, and highly processed foods.

Throughout the book, readers are presented with numerous resources that are all extensions of the lower energy density approach, including food energy density tables, visual comparisons of calorie-matched meals, and simple meal suggestions, recipes, and food swaps that favor energy density reductions. Each chapter in Volumetrics represents one week of the program—to be read progressively—and readers are introduced to a new theme each week. After the explanatory content has been covered, the second half of Volumetrics is dedicated exclusively to recipes and printable materials such as food lists, kitchen charts, daily record sheets, food and symptom diaries, and ‘SMART’ goals (Specific, Measurable, Achievable, Realistic, and Timely).

Condition targeted by the book, if applicable

The Ultimate Volumetrics Diet primarily targets body weight management and weight loss.

Apparent target audience of the book

The target audience for The Ultimate Volumetrics Diet are people wanting to achieve and maintain a healthy body weight. The emphasis in the book, however, is placed on weight loss strategies for people that are overweight or obese.

Criterion 3.1. Is the intervention likely to improve the target condition?

3 out of 4

Volumetrics received a score of 3, indicating that relevant evidence suggests the proposed intervention is likely to moderately improve the target condition in the medium-to-long term (6+ months). Rolls published a 12-month trial in which a diet similar to the one described in the book led to 17 pounds of weight loss in women with obesity over 12 months. However, the effectiveness of the diet doesn’t stand out relative to other weight loss diets, and the effectiveness of all diets tends to wane in the long run. The scientific evidence on this is discussed at greater length in the Scientific Accuracy section of this book review.

People who are already at a healthy body weight will likely maintain their body weight (or possibly lose a few pounds), while those starting as overweight or obese will likely experience greater weight loss over 6-12 months.

The Volumetrics diet is likely to cause a calorie deficit due to the shift away from energy dense and highly processed food products. Volumetrics also assists with changing behavior by providing readers with a general overview of their calorie needs for weight loss (based on the American Dietetic Association’s position statement on Weight Management), some 4-week sample menus and meal strategies for each calorie-level, and it instructs users to adjust their calorie intake in accordance with their body weight change during the program. The combination of calorie tracking, or at least following calorie-controlled menus, alongside the prioritization on eating filling and nutritious foods, should promote weight loss and improve the target condition in the target audience.

Criterion 3.2. Is the intervention likely to improve general health in the target audience?

4 out of 4

Volumetrics received a score of 4, indicating the relevant evidence suggests the intervention proposed is likely to greatly improve general health in the medium-to-long term (6+ months). The recommendations largely align with common dietary recommendations for improving general health, despite Volumetrics not necessarily advertising itself as a health-promoting book. Volumetrics emphasizes the need to prioritize minimally processed and nutritious foods (primarily plants) and restrict fatty meats, high-fat dairy, and highly processed foods, which are all recommendations that closely align with National Dietary Guidelines of most countries worldwide. We assume this is not a coincidence, but in any case, prospective cohort studies have shown that closer adherence to the dietary guidelines is associated with a lower risk of cardiovascular disease and all-cause mortality.

Compared to typical affluent diets, following Volumetrics recommendations will allow most people to better control their energy intake (to manage body weight) and reduce their salt, trans fat, saturated fat, and sugar intake. These are all dietary improvements with strong evidence, especially when combined and adhered to, that mitigate the risk of chronic diseases.

Criterion 3.3. Does the diet portion of the intervention promote an adequate nutrient intake for general health in the target audience?

4 out of 4

Volumetrics received a score of 4, indicating that the intervention diet will likely provide adequate levels of all relevant nutrients in the target audience and a level of nonessential health-promoting nutrients that is superior to typical diets over the medium-to-long term (6+ months). Provided the reader consumes a diverse range of the recommended foods (which is advised), an abundance of essential and non-essential nutrients will be hard to avoid.

Unlike many diets, Volumetrics does not recommend severely restricting or eliminating any key food(s) that would otherwise make it difficult to obtain essential nutrients. Volumetrics also warns dieters who opt for very-low-calorie intakes that calorie intake should never go below 1200kcal per day as it “becomes too difficult to meet all of your nutrition needs.” [Page 12]. However, we aren’t concerned about this since this level of calorie intake is far too low to be sustainable. Even if someone were to adopt this level of restriction for the initial weight loss phase, calorie intake would have to increase eventually.

The only concern for nutrient sufficiency worth mentioning is for readers that happen to choose both the lowest calorie intake (1200 – 1500 kcal per day) and the lowest protein recommendation (10% of daily calories). In this case, protein intake can get down to as low as 30 grams per day. We have decided not to deduct a point for this reason, though, as this level of caloric restriction is necessarily temporary and the suggested meals in the book are sufficient in dietary protein.

Overall (average) score for healthfulness

3.7 out of 4