Declining rates of physical activity in the United States: what are the contributors?

This review describes current patterns and long-term trends (up to 50 years when possible) related to (a) physical activity, (b) employment and occupation, (c) travel behavior, (d) land use, and (e) related behaviors (e.g., television watching). On the basis of available data, the following trends were observed according to type of physical activity: relatively stable or slightly increasing levels of leisure-time physical activity, declining work-related activity, declining transportation activity, declining activity in the home, and increasing sedentary activity. These result in an overall trend of declining total physical activity. Large differences were noted in the rates of walking for transportation across metropolitan statistical areas. A strong linear increase existed in vehicle miles traveled per person over the past half century, coupled with a strong and consistent trend toward Americans living in suburbs. Although it is difficult to precisely quantify owing to the lack of long-term data, it is apparent that a combination of changes to the built environment and increases in the proportion of the population engaging in sedentary activities put the majority of the American population at high risk of physical inactivity.

Further validation and reliability testing of the Trust in Physician Scale. The Stanford Trust Study Physicians

OBJECTIVES

To further validate and assess the reliability and validity of the Trust in Physician Scale.

METHODS

Consecutive adult patients (n = 414) from 20 community-based, primary care practices were enrolled in a prospective, 6-month study. At enrollment, subjects completed the 11-item Trust in Physician Scale plus measures of demographics, preferences for care, and satisfaction with care received from the physician. Continuity, satisfaction with care, and self-reported adherence to treatment were measured at 6 months. Reliability, construct validity, and predictive validity were assessed using correlation coefficients and analysis of variance techniques.

RESULTS

The Trust in Physician Scale showed high internal consistency (Cronbach's alpha = .89) and good 1-month test-retest reliability (intraclass correlation coefficient = .77). As expected, trust increased with the length of the relationship and was higher among patients who actively chose their physician, who preferred more physician involvement, and who expected their physician to care for a larger proportion of their problems (P < 0.001 for all associations). Baseline trust predicted continuity with the physician, self-reported adherence to medication, and satisfaction at 6 months after adjustment for gender, age, education, length of the relationship, active choice of the physician, and preferences for care. After additional adjustment for baseline satisfaction with physician care, trust remained a significant predictor of continuity, adherence, and satisfaction.

CONCLUSIONS

The Trust in Physician Scale has desirable psychometric characteristics and demonstrates construct and predictive validity. It appears to be related to, but still distinct from, patient satisfaction with the physician and, thus, provides a valuable additional measure for assessment of the quality of the patient-physician relationship.

Network analysis in public health: history, methods, and applications

Network analysis is an approach to research that is uniquely suited to describing, exploring, and understanding structural and relational aspects of health. It is both a methodological tool and a theoretical paradigm that allows us to pose and answer important ecological questions in public health. In this review we trace the history of network analysis, provide a methodological overview of network techniques, and discuss where and how network analysis has been used in public health. We show how network analysis has its roots in mathematics, statistics, sociology, anthropology, psychology, biology, physics, and computer science. In public health, network analysis has been used to study primarily disease transmission, especially for HIV/AIDS and other sexually transmitted diseases; information transmission, particularly for diffusion of innovations; the role of social support and social capital; the influence of personal and social networks on health behavior; and the interorganizational structure of health systems. We conclude with future directions for network analysis in public health.

Systems science methods in public health: dynamics, networks, and agents

Complex systems abound in public health. Complex systems are made up of heterogeneous elements that interact with one another, have emergent properties that are not explained by understanding the individual elements of the system, persist over time, and adapt to changing circumstances. Public health is starting to use results from systems science studies to shape practice and policy, for example in preparing for global pandemics. However, systems science study designs and analytic methods remain underutilized and are not widely featured in public health curricula or training. In this review we present an argument for the utility of systems science methods in public health, introduce three important systems science methods (system dynamics, network analysis, and agent-based modeling), and provide three case studies in which these methods have been used to answer important public health science questions in the areas of infectious disease, tobacco control, and obesity.

Public health program capacity for sustainability: a new framework

Background

Public health programs can only deliver benefits if they are able to sustain activities over time. There is a broad literature on program sustainability in public health, but it is fragmented and there is a lack of consensus on core constructs. The purpose of this paper is to present a new conceptual framework for program sustainability in public health.

Methods

This developmental study uses a comprehensive literature review, input from an expert panel, and the results of concept-mapping to identify the core domains of a conceptual framework for public health program capacity for sustainability. The concept-mapping process included three types of participants (scientists, funders, and practitioners) from several public health areas (e.g., tobacco control, heart disease and stroke, physical activity and nutrition, and injury prevention).

Results

The literature review identified 85 relevant studies focusing on program sustainability in public health. Most of the papers described empirical studies of prevention-oriented programs aimed at the community level. The concept-mapping process identified nine core domains that affect a program’s capacity for sustainability: Political Support, Funding Stability, Partnerships, Organizational Capacity, Program Evaluation, Program Adaptation, Communications, Public Health Impacts, and Strategic Planning. Concept-mapping participants further identified 93 items across these domains that have strong face validity—89% of the individual items composing the framework had specific support in the sustainability literature.

Conclusions

The sustainability framework presented here suggests that a number of selected factors may be related to a program’s ability to sustain its activities and benefits over time. These factors have been discussed in the literature, but this framework synthesizes and combines the factors and suggests how they may be interrelated with one another. The framework presents domains for public health decision makers to consider when developing and implementing prevention and intervention programs. The sustainability framework will be useful for public health decision makers, program managers, program evaluators, and dissemination and implementation researchers.

Sustainability of evidence-based healthcare: research agenda, methodological advances, and infrastructure support

BACKGROUND

Little is known about how well or under what conditions health innovations are sustained and their gains maintained once they are put into practice. Implementation science typically focuses on uptake by early adopters of one healthcare innovation at a time. The later-stage challenges of scaling up and sustaining evidence-supported interventions receive too little attention. This project identifies the challenges associated with sustainability research and generates recommendations for accelerating and strengthening this work.

METHODS

A multi-method, multi-stage approach, was used: (1) identifying and recruiting experts in sustainability as participants, (2) conducting research on sustainability using concept mapping, (3) action planning during an intensive working conference of sustainability experts to expand the concept mapping quantitative results, and (4) consolidating results into a set of recommendations for research, methodological advances, and infrastructure building to advance understanding of sustainability. Participants comprised researchers, funders, and leaders in health, mental health, and public health with shared interest in the sustainability of evidence-based health care.

RESULTS

Prompted to identify important issues for sustainability research, participants generated 91 distinct statements, for which a concept mapping process produced 11 conceptually distinct clusters. During the conference, participants built upon the concept mapping clusters to generate recommendations for sustainability research. The recommendations fell into three domains: (1) pursue high priority research questions as a unified agenda on sustainability; (2) advance methods for sustainability research; (3) advance infrastructure to support sustainability research.

CONCLUSIONS

Implementation science needs to pursue later-stage translation research questions required for population impact. Priorities include conceptual consistency and operational clarity for measuring sustainability, developing evidence about the value of sustaining interventions over time, identifying correlates of sustainability along with strategies for sustaining evidence-supported interventions, advancing the theoretical base and research designs for sustainability research, and advancing the workforce capacity, research culture, and funding mechanisms for this important work.

Shaping the context of health: a review of environmental and policy approaches in the prevention of chronic diseases

Given the growing attention on how environmental and policy interventions can affect chronic disease burden, our objectives are to describe (a) effective and promising interventions to address tobacco use, physical activity, and healthy eating and (b) lessons learned from the literature and practice experience in applying environmental and policy approaches. A total of 17 interventions were reviewed, organized across 3 domains affecting the physical environment/access, economic environment, and communication environment. Many of these interventions are effective. Several lessons are important to consider, such as the need to start with environmental and policy approaches, intervene comprehensively and across multiple levels, make use of economic evaluations, make better use of existing analytic tools, understand the politics and local context, address health disparities, and conduct sound policy research.

The Program Sustainability Assessment Tool: a new instrument for public health programs

INTRODUCTION

Public health programs can deliver benefits only if they are able to sustain programs, policies, and activities over time. Although numerous sustainability frameworks and models have been developed, there are almost no assessment tools that have demonstrated reliability or validity or have been widely disseminated. We present the Program Sustainability Assessment Tool (PSAT), a new and reliable instrument for assessing the capacity for program sustainability of various public health and other programs.

METHODS

A measurement development study was conducted to assess the reliability of the PSAT. Program managers and staff (n = 592) representing 252 public health programs used the PSAT to rate the sustainability of their program. State and community-level programs participated, representing 4 types of chronic disease programs: tobacco control, diabetes, obesity prevention, and oral health.

RESULTS

The final version of the PSAT contains 40 items, spread across 8 sustainability domains, with 5 items per domain. Confirmatory factor analysis shows good fit of the data with the 8 sustainability domains. The subscales have excellent internal consistency; the average Cronbach's α is 0.88, ranging from 0.79 to 0.92. Preliminary validation analyses suggest that PSAT scores are related to important program and organizational characteristics.

CONCLUSION

The PSAT is a new and reliable assessment instrument that can be used to measure a public health program's capacity for sustainability. The tool is designed to be used by researchers, evaluators, program managers, and staff for large and small public health programs.

Methods for analysing the breakdown of food in human mastication

A method is described for measuring the rate at which carrot particles are broken down in chewing. In 10 subjects, this rate declined progressively throughout mastication. This was analysed in terms of two variables: (a) the intra-oral selection of particles for fracture, (b) the size distribution of fractured pieces of those particles. When intra-oral selection was measured by different methods, it depended mainly upon particle size. The selection of small particles might depend on the number of chews taken after the food was placed in the mouth. The size distribution of fractured pieces was obtained from one chew on three different particle sizes. These distributions were partially described by two different equations whose characteristics suggest that carrot particles are subjected to only one breakage per chew and that the number of fragments formed per breakage is small. It is suggested that the cusps present on the post-canines were important in determining this breakage pattern, and that the dependence of selection on particle size was primarily responsible for the decline in the rate of breakdown with increasing numbers of chews.

Sleep and circadian influences on cardiac autonomic nervous system activity

To assess the separate contributions of the sleep and circadian systems to changes in cardiac autonomic nervous system (ANS) activity, 12 supine subjects participated in two 26-h constant routines, which were counterbalanced and separated by 1 wk. One routine did not permit sleep, whereas the second allowed the subjects to sleep during their normal sleep phase. Parasympathetic nervous system activity was assessed with respiratory sinus arrhythmia as measured from the spectral analysis of cardiac beat-to-beat intervals. Sympathetic nervous system activity was primarily assessed with the preejection period as estimated from impedance cardiography, although the 0.1-Hz peak from the spectral analysis of cardiac beat-to-beat intervals, the amplitude of the T wave in the electrocardiogram, and heart rate were also measured. Respiratory sinus arrhythymia showed a 24-h rhythm independent of sleep, whereas preejection period only showed a 24-h rhythm if sleep occurred. Thus the findings indicate that parasympathetic nervous system activity is mostly influenced by the circadian system, whereas sympathetic nervous system activity is mostly influenced by the sleep system.

TOCOTRIENOL OFFERS BETTER PROTECTION THAN TOCOPHEROL FROM FREE RADICAL-INDUCED DAMAGE OF RAT BONE

1. Free radicals generated by ferric nitrilotriacetate (FeNTA) can activate osteoclastic activity and this is associated with elevation of the bone resorbing cytokines interleukin (IL)-1 and IL-6. In the present study, we investigated the effects of 2 mg/kg FeNTA (2 mg iron/kg) on the levels of serum IL-1 and IL-6 with or without supplementation with a palm oil tocotrienol mixture or alpha-tocopherol acetate in Wistar rats. 2. The FeNTA was found to elevate levels of IL-1 and IL-6. Only the palm oil tocotrienol mixture at doses of 60 and 100 mg/kg was able to prevent FeNTA-induced increases in IL-1 (P < 0.01). Both the palm oil tocotrienol mixture and alpha-tocopherol acetate, at doses of 30, 60 and 100 mg/kg, were able to reduce FeNTA-induced increases in IL-6 (P < 0.05). Therefore, the palm oil tocotrienol mixture was better than pure alpha-tocopherol acetate in protecting bone against FeNTA (free radical)-induced elevation of bone-resorbing cytokines. 3. Supplementation with the palm oil tocotrienol mixture or alpha-tocopherol acetate at 100 mg/kg restored the reduction in serum osteocalcin levels due to ageing, as seen in the saline (control) group (P < 0.05). All doses of the palm oil tocotrienol mixture decreased urine deoxypyridinoline cross-link (DPD) significantly compared with the control group, whereas a trend for decreased urine DPD was only seen for doses of 60 mg/kg onwards of alpha-tocopherol acetate (P < 0.05). 4. Bone histomorphometric analyses have shown that FeNTA injections significantly lowered mean osteoblast number (P < 0.001) and the bone formation rate (P < 0.001), but raised osteoclast number (P < 0.05) and the ratio of eroded surface/bone surface (P < 0.001) compared with the saline (control) group. Supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent all these FeNTA-induced changes, but a similar dose of alpha-tocopherol acetate was found to be effective only for mean osteoclast number. Injections of FeNTA were also shown to reduce trabecular bone volume (P < 0.001) and trabecular thickness (P < 0.05), whereas only supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent these FeNTA-induced changes.

Disparities in tobacco marketing and product availability at the point of sale: Results of a national study

OBJECTIVE

Neighborhood socioeconomic and racial/ethnic disparities exist in the amount and type of tobacco marketing at retail, but most studies are limited to a single city or state, and few have examined flavored little cigars. Our purpose is to describe tobacco product availability, marketing, and promotions in a national sample of retail stores and to examine associations with neighborhood characteristics.

METHODS

At a national sample of 2230 tobacco retailers in the contiguous US, we collected in-person store audit data on: Availability of products (e.g., flavored cigars), quantity of interior and exterior tobacco marketing, presence of price promotions, and marketing with youth appeal. Observational data were matched to census tract demographics.

RESULTS

Over 95% of stores displayed tobacco marketing; the average store featured 29.5 marketing materials. 75.1% of stores displayed at least one tobacco product price promotion, including 87.2% of gas/convenience stores and 85.5% of pharmacies. 16.8% of stores featured marketing below three feet, and 81.3% of stores sold flavored cigars, both of which appeal to youth. Stores in neighborhoods with the highest (vs. lowest) concentration of African-American residents had more than two times greater odds of displaying a price promotion (OR=2.1) and selling flavored cigars (OR=2.6). Price promotions were also more common in stores located in neighborhoods with more residents under age 18.

CONCLUSIONS AND RELEVANCE

Tobacco companies use retail marketing extensively to promote their products to current customers and youth, with disproportionate targeting of African Americans. Local, state, and federal policies are needed to counteract this unhealthy retail environment.

Optimum mouthful for food comminution in human mastication

The effect of varying the portion of food offered for chewing (termed the mouthful) on aspects of the oral comminution of salted peanuts was investigated on six human subjects. Particle-size distributions, assessed from a sieving analysis, were similar for different mouthfuls, and could be characterized by a sieve size that would pass 80 per cent of the particles by volume in a distribution. As the food weight was increased, (a) the rate of particle-size reduction of the food declined exponentially, (b) the rate of food surface area production increased, (c) the number of chews to swallow the food increased, (d) the number of chews per unit gram to swallow the food decreased, (e) the food-particle sizes that were swallowed increased. It is hypothesized that the volume of food between the teeth at any chewing stroke depends more on food-particle size than on the weight of food in the mouth. The swallowing of small mouthfuls of peanuts may have depended more on the time to wet particles with saliva than particle size.

Atrial myxoma: national incidence, diagnosis and surgical management

Despite being the most common benign intracardiac tumour with an excellent prognosis after surgical excision the incidence of atrial myxoma (except at autopsy) is unknown. We reviewed all patients admitted to the National Cardiac Surgery Unit (n = 26) with an atrial myxoma over a fifteen year period (1977-1991) to compile national incidence data and assess pre-operative diagnosis, management, surgical technique, and outcome. Preoperative symptoms were: congestive cardiac failure (12 patients), embolism (8 patients), constitutional (3 patients), asymptomatic (2 patients) and tachyarrhythmia (1 patient). The diagnosis was confirmed by 2D echocardiography alone in thirteen patients and by a combination of echocardiography and angiography in thirteen patients. At operation the site of the tumour was left atrial in 24 patients and bi-atrial in two patients. All cases were confirmed by histology. All patients made a good post-operative recovery, although one patient survived a pulmonary embolus and one patient developed a deep venous thrombosis. There has been one late death (five months after surgery) from a cerebrovascular accident. Serial echocardiography has revealed one recurrence to date (8 years after surgery). The surgical incidence of these tumours in the Republic of Ireland over the study period was 0.5 atrial myxomas/million population/year. Although rare atrial myxomas are the most important cardiac tumours to diagnose as the results from surgery are excellent.

HIV risk behaviours among male-to-female transgenders in comparison with homosexual or bisexual males and heterosexual females

Issues and concerns among six directors, one counsellor and one consultant for transgender programmes in San Francisco are described. Additionally, 173 clients who were enrolled in programmes in eight AIDS service organizations were interviewed using a structured survey questionnaire. This study examined the relationships between HIV risk behaviours and social and cognitive factors among transgendered females (male-to-female transgenders) (n = 25) in comparison with homosexual or bisexual males (n = 122) and heterosexual females (n = 26). Transgendered females engaged in riskier behaviours than the other groups in terms of the number of sex partners in the past 30 days and the past six months, commercial sex activities, and having a steady sex partner who injected drugs. Adverse socioeconomic conditions and transgender-specific risk behaviours such as injecting hormones in relation to HIV risk behaviours must be targeted by future intervention studies.

Designing for Dissemination and Sustainability to Promote Equitable Impacts on Health

Designing for dissemination and sustainability (D4DS) refers to principles and methods for enhancing the fit between a health program, policy, or practice and the context in which it is intended to be adopted. In this article we first summarize the historical context of D4DS and justify the need to shift traditional health research and dissemination practices. We present a diverse literature according to a D4DS organizing schema and describe a variety of dissemination products, design processes and outcomes, and approaches to messaging, packaging, and distribution. D4DS design processes include stakeholder engagement, participatory codesign, and context and situation analysis, and leverage methods and frameworks from dissemination and implementation science, marketing and business, communications and visualarts, and systems science. Finally, we present eight recommendations to adopt a D4DS paradigm, reflecting shifts in ways of thinking, skills and approaches, and infrastructure and systems for training and evaluation.

Getting the big picture in community science: methods that capture context

Community science has a rich tradition of using theories and research designs that are consistent with its core value of contextualism. However, a survey of empirical articles published in the American Journal of Community Psychology shows that community scientists utilize a narrow range of statistical tools that are not well suited to assess contextual data. Multilevel modeling, geographic information systems (GIS), social network analysis, and cluster analysis are recommended as useful tools to address contextual questions in community science. An argument for increased methodological consilience is presented, where community scientists are encouraged to adopt statistical methodology that is capable of modeling a greater proportion of the data than is typical with traditional methods.

Is food particle size a criterion for the initiation of swallowing?

A small study on fifteen subjects found that brazil nut particles always broke down much more rapidly per chew than raw carrot particles. Both foods were swallowed, on average, after similar numbers of chews. However, a relationship was found which suggested that subjects that swallowed after few chews took less for carrots than brazils and vice versa for those that took more chews. An extended study with carrot showed a significant correlation between the rate of size breakdown and the number of chews required for swallowing in dentate subjects (r = 0.69) but not in full denture wearers. The whole sample (n = 79 including six wearers of partial dentures) gave a significant correlation of r = 0.65. It is concluded that some consideration of the physical properties (texture) of foods is necessary before results from this type of study can be interpreted as relevant or not for dentistry.

The Translational Science Benefits Model: A New Framework for Assessing the Health and Societal Benefits of Clinical and Translational Sciences

We report the development of the Translational Science Benefits Model (TSBM), a framework designed to support institutional assessment of clinical and translational research outcomes to measure clinical and community health impacts beyond bibliometric measures. The TSBM includes 30 specific and potentially measurable indicators that reflect benefits that accrue from clinical and translational science research such as products, system characteristics, or activities. Development of the TSBM was based on literature review, a modified Delphi method, and in‐house expert panel feedback. Three case studies illustrate the feasibility and face validity of the TSBM for identification of clinical and community health impacts that result from translational science activities. Future plans for the TSBM include further pilot testing and a resource library that will be freely available for evaluators, translational scientists, and academic institutions who wish to implement the TSBM framework in their own evaluation efforts.

Perceptions of neighborhood environment for physical activity: is it "who you are" or "where you live"?

Lack of physical activity among American adults is a serious public health concern. Many factors influence activity levels, and most research has focused on either individual factors, such as race and income, or on characteristics of the physical environment, such as the availability of parks. Our study used a cross-sectional multilevel design to examine the influences of individual- and neighborhood-level characteristics on participant's perceptions of their neighborhood as an appropriate venue for physical activity. Study participants were 1,073 African American and white adults living in the St. Louis, Missouri, metropolitan area. Individual-level information was gathered from self-administered questionnaires; neighborhood-level data for these same individuals were obtained from the 2000 US Census. We found that both individual and neighborhood characteristics were significant predictors of how individuals perceived physical activity opportunities in their neighborhood, and that African Americans perceived their neighborhoods as less safe and less pleasant for physical activity than did whites, regardless of the racial composition of the neighborhood. We suggest that any evaluation of opportunities for physical activity within a neighborhood should include consideration of resident's perceptions of the safety and pleasantness of using them, and that the role of perceived and actual neighborhood conditions in explaining disparities in physical activity between African American and other populations should be examined further.

Smoke signs: patterns of tobacco billboard advertising in a metropolitan region

OBJECTIVE

To use geographic information systems data and analyses to describe locations and characteristics of tobacco billboards in a large metropolitan area, and to assess the extent to which tobacco companies are locating billboards in close proximity to minority neighbourhoods and schools.

DESIGN

Observational study of billboards in a large metropolitan region.

SETTING

City and county of St Louis, Missouri.

PARTICIPANTS

All stationary billboards in the city and county of St Louis were eligible to be observed, with the exception of bus stop and street side retail advertising signs (for example, cigarette advertising at gas stations). A total of 1239 non-blank billboards were observed. All data were collected in early 1998.

MAIN OUTCOME MEASURES

Tobacco and non-tobacco billboard geographic distribution; billboard type and product brand frequencies; and billboard neighbourhood characteristics.

RESULTS

Almost 20% of the billboards contained tobacco advertising. Four of the top five and nine of the top 22 brands displayed on billboards were tobacco products. Billboards were located in all areas of St Louis except for the communities with the highest average incomes. Tobacco billboards were more likely to be found in low income areas and areas with a higher percentage of African Americans. Images of African American figures on tobacco billboards were concentrated in the most heavily African American populated regions of the city. Approximately 74% of all billboards in the city of St Louis were within 2000 feet (700 metres) of public school property.

CONCLUSIONS

Tobacco products were the single most heavily advertised type of product on billboards in St Louis. The geographic distribution of tobacco billboards, as well as the types of images found on these billboards, is consistent with the hypothesis that tobacco companies are targeting poor and minority communities with their advertising. Methods employing geographic information systems are a powerful technique for examining outdoor tobacco advertising.

Inequalities in tobacco outlet density by race, ethnicity and socioeconomic status, 2012, USA: results from the ASPiRE Study

BACKGROUND

Evidence of racial/ethnic inequalities in tobacco outlet density is limited by: (1) reliance on studies from single counties or states, (2) limited attention to spatial dependence, and (3) an unclear theory-based relationship between neighbourhood composition and tobacco outlet density.

METHODS

In 97 counties from the contiguous USA, we calculated the 2012 density of likely tobacco outlets (N=90 407), defined as tobacco outlets per 1000 population in census tracts (n=17 667). We used 2 spatial regression techniques, (1) a spatial errors approach in GeoDa software and (2) fitting a covariance function to the errors using a distance matrix of all tract centroids. We examined density as a function of race, ethnicity, income and 2 indicators identified from city planning literature to indicate neighbourhood stability (vacant housing, renter-occupied housing).

RESULTS

The average density was 1.3 tobacco outlets per 1000 persons. Both spatial regression approaches yielded similar results. In unadjusted models, tobacco outlet density was positively associated with the proportion of black residents and negatively associated with the proportion of Asian residents, white residents and median household income. There was no association with the proportion of Hispanic residents. Indicators of neighbourhood stability explained the disproportionate density associated with black residential composition, but inequalities by income persisted in multivariable models.

CONCLUSIONS

Data from a large sample of US counties and results from 2 techniques to address spatial dependence strengthen evidence of inequalities in tobacco outlet density by race and income. Further research is needed to understand the underlying mechanisms in order to strengthen interventions.

The significance of cusps

It has been argued that the prolonged retention of cusps in the human dentition is a relatively recent aberration due to the negligible abrasiveness of modern diets and that to achieve maximum efficiency and freedom from disease human teeth should be worn down as they are in many herbivorous mammals. Here we critically review the evidence that has been put forward to support this idea and, after discussing the design of occlusal surfaces in relation to the wide variety of mammalian diets, we conclude that cusps are adaptations for breaking food with specific physical properties.