The body mass index is a simple calculation that takes a person’s weight in kilograms and divides it by the height in meters squared. Overweight is defined as a BMI of 25-29.9, and obesity is defined as a BMI of 30 or more. A recent study conducted by the American College of Foot & Ankle Surgeons on 220 patients (31 males and 189 females) readily showed that the foot and ankle are considerably affected by an increase in BMI. Using the 36-Item Short Form Health Survey from the Medical Outcomes Study, the SF-36, the patients were given a self-assessment of their overall health. This commonly used patient-based outcome instrument has been found to be a valid method for measuring perceived physical and mental health constructs for a wide range of patient groups. The study found that patients with a BMI under 25 only had a 5% incidence of foot pain, while the group with a BMI over 30 had a 50% incidence of foot pain. The group with a BMI over 30 also had significantly lower scores for each of the 8 different subscales of the SF-36, which included physical functioning, role-physical, bodily pain, general health, vitality, social functioning, role-emotional, and mental health. This shows that an increase in BMI has a detrimental effect on all aspects of health in the foot and ankle, as well as on overall health.
The number of overweight and obese people in the United States has steadily increased over the past few decades to the point where approximately 60% of the adult population is overweight and 74% of the overweight population is afflicted with painful musculoskeletal conditions, with degenerative joint disease and osteoarthritis being the most prominent conditions. This can not only lead to increased pain on the weightbearing surface of the foot and ankle, but also to a more sedentary lifestyle which further exacerbates the obesity problem. For this reason, it is imperative for foot and ankle surgeons to recognize the importance of maintaining a healthy weight in their patients, as well as to serve as an example to their patients by maintaining a healthy weight themselves. This article will discuss the effects of obesity on foot and ankle function, as well as provide strategies for surgeons and their patients to achieve a healthy body mass index (BMI).
Understanding the Relationship between Weight and Foot/Ankle Pain
The next step in successfully combating foot and ankle pain is to understand the relationship between weight and foot function. Much speculation exists on the topic, with some experts contending that obesity is a root cause of many foot conditions, while others argue that it is only an exacerbating factor. Still, others believe that there is no relationship at all. In fact, there is overwhelming research that indicates that weight has a profound effect on the normal function of the foot. As the total weight of the body increases, as seen in the obese, there is also an increase in the force the foot must absorb with each step. This means that the foot must work harder and in a less efficient manner to do its job. The additional stress on the foot often causes painful conditions. One of the most important changes to occur in the foot as a result of increased weight is the collapse of the arch. The arch of the foot is formed by bones held together by their shape and the tight grouping of ligaments and is supported by the muscles and tendons. The most dramatic effect of weight bearing is seen at the talonavicular joint, which is the keystone of the arch. Here the increased pressure on the arch causes a “flattening” of the foot, and an inward collapse of the ankle often occurs. This “overpronation” is a determining factor for the development of painful foot conditions.
Excess Weight and the Pressure on Feet and Ankles
The increased stress on the ankle and foot from weight gain does not affect just the soft tissue over time. Edema and overpronation associated with obesity are very common and can create long-term damage in the ankle and foot. Patients often complain of arthritis-like symptoms in the midfoot with sharp pain. This is due to increased pressure on the joint from above and further damage from increased stress underneath due to altered biomechanics. Studies have shown a strong relationship between increased BMI and symptomatic osteoarthritis in the foot and ankle. Patients with a BMI > 35 are 10 times more likely to develop end-stage ankle osteoarthritis. Weight-related joint disease in the foot and ankle is somewhat preventable with weight reduction. Then again, adherence to weight loss remains its only drawback to this conservative treatment plan. Failed attempts at trying to return to a healthy weight and recurrent weight gain make treatment of the joint disease very difficult, and often surgical management of the disease is required. High success rates for pain relief and improved functional outcomes have been reported with realignment and fusion-type surgical procedures for the management of end-stage ankle osteoarthritis in the obese patient.
Effects of Weight on Foot and Ankle Joints
There are a number of effects on joints at various sites in the body, and it is easy to understand that the joints in the lower limbs are those most likely to be affected by added load. Every 1 pound of weight translates to 2-3 pounds of added stress on the knees, and 6-7 times the body weight load is exerted across the ankle joint when walking. This altered biomechanical load has been shown to put a great strain on the joints. Increased weight is a known risk factor for development of osteoarthritis, a degenerative joint disease. It has been shown in the Framingham study that being as little as 10 pounds overweight doubles the risk of developing symptomatic osteoarthritis of the knee. 43% of the osteoarthritis in the knee for this group was attributed to their weight status. Similar correlations have been found between increased weight and osteoarthritis of the ankle, and hindfoot arthritis, although not as conclusively as for the knee. A recent systematic review and meta-analysis found that overweight and obese persons have an increased risk of developing rheumatoid arthritis compared to persons of normal BMI. Osteoarthritis as a result of the degenerative consequences of increased joint stress is often a terminal event necessitating foot or ankle fusion or severe arthrodesis. This should be borne in mind when considering management of pain originating from end stage arthritis.
Strategies for Maintaining a Healthy BMI
A representative study using an evidence-based weight loss intervention has shown that an increase in fruit and vegetable intake is the best dietary strategy for short and long-term weight management. High fruit and vegetable intake is inversely associated with a change in weight.
A study involving dietary strategies for preventing regaining weight by overweight Finnish men and women found that a diet with a low energy density combined with low fat consumption resulted in the greatest weight loss and smaller weight regain over a 4-year period. This can be achieved with an increase in fruit and vegetable intake and a decrease in fat intake, as fat has a higher energy density compared to carbohydrates and protein.
Step one in the dietary strategy is to reduce energy intake and fat intake, with step two being an increase in vegetable intake. High intake of dietary fats and low intake of vegetables have been shown to have an inverse relationship with BMI. High-fat intake often results in higher energy intake due to fat consumed having low satiety. Energy density, which is the amount of energy in a given weight of food, is also positively related to energy intake.
Macronutrient distribution involving a balanced intake of carbohydrate, protein, and unsaturated fat has been shown to help in weight control. Low carbohydrate diets have shown mixed results, with some reporting rapid weight loss and no difference in energy expenditure compared to high carbohydrate, low-fat diets, yet others have shown the potential for an increased risk of chronic diseases. Compared to protein and carbohydrates, fats have been associated with a higher energy intake due to fat intake increasing palatability or consumption of food. This has led to the intake of high-fat food consuming a larger portion of total energy intake.
Maintaining a healthy BMI for those who are already at a healthy weight or those who are overweight is a difficult task with the energy balance equation guidelines of increasing energy expenditure and limiting caloric intake. However, a recent review on the impact of weight on foot and ankle pain provides an engaging look at how to minimize weight-related foot and ankle pain through maintaining a healthy BMI. Dietary strategies are necessary for losing weight or maintaining a healthy weight. Macronutrient and macronutrient distribution are an important part of dietary strategies.
Healthy Eating Habits and Portion Control
This is especially helpful when it comes to foot and ankle pain because it usually is very heavy in relation to specific weight bearing muscles and tendons. Knowing this, by calculating a specific individual’s BMI and comparing it to the weight status categories, one can determine how much weight they need to lose to fall into the normal weight range. This is the first step in understanding how to relieve foot and ankle pain.
An individual with a BMI of less than 18.5 is considered underweight. A BMI between 18.5 – 24.9 is considered normal weight. Overweight is categorized as a BMI of 25 – 29.9, and obesity is anything above 30. BMI is not a diagnostic tool, but instead an indicator which is used to screen for weight categories that may lead to health problems.
It is important to first understand what a “healthy” weight is for any individual. Body Mass Index (BMI) is a tool that is used to determine healthy weight for individuals by comparing their weight to their height. BMI is calculated by a mathematical formula that takes into account individuals’ height and weight. The formula used to calculate BMI is weight / (height^2) x 703. Weight status categories are then broken down into different ranges.
Regular Physical Activity and Exercise
In order to lose weight or maintain a healthy weight after weight loss, people must do more than 60 minutes of moderate to intense intensity activity on most days. Usually, it’s best to do 5-7 days of activity each week and continue this level of activity for an extended time. To get the best results, when the to-be weight manager is able, it is advised to progress to 60-90 minutes of moderate-intense intensity activity on most days, in combination with a reduced calorie intake. This amount of exercise will also help to keep away the weight regain and changes to the body composition due to the prevention of a lower metabolic rate usually associated with weight loss. High levels of physical activity will be most possible for people with a high amount of weight loss (when it is easier to move and have a lower risk of joint injury) and with the consumption of few calorie-dense foods. High-intensity activities (which would be best to be intervals when low fitness levels improve) and an increase in the amount of time spent performing these activities can lead to even greater weight loss and changes in body composition, provided that the individual can tolerate these levels of activity.
That said, greater health benefits can be gained by engaging in a moderate amount of physical activity (e.g. 60 minutes or more of moderate-intensity activity on most days of the week) or more, which could mean improving the intensity or the amount of time spent. The addition of muscle-strengthening activities two or more days per week, as health permits, is also of great benefit.
Regular physical activity is essential in controlling weight and improving overall health. For people who are overweight or obese, the benefits of engaging in at least 60 minutes of moderate-intensity activity a day cannot be overstated.
Seeking Professional Guidance for Weight Management
Professional guidance is strongly advised for patients who have had difficulty losing weight on their own. A health professional will assess the patient’s lifestyle and the factors that are contributing to obesity. They will identify the patient’s readiness to make behavioral changes and help set achievable goals for weight management. Assessment of the patient’s diet and eating habits is an essential component of weight management. Based on nutritional assessment, a dietitian can guide the patient in dietary changes that are necessary for weight loss and provide education in basic nutrition and healthy eating. Decreasing or avoiding high-calorie foods and increasing intake of whole grains, fruits, and vegetables is recommended. Changes should be achievable and sustainable, thus dietitians often assist in setting short-term goals that act as stepping stones to the long-term goal. The dietitian can also help the patient to monitor their food intake by keeping a food diary, which is useful for identifying eating behaviors that contribute to obesity. Regular review and monitoring of the patient’s body weight and making adjustments to the meal plan is important to facilitate continual weight loss over time. This can be done in collaboration with the patient’s GP on a Chronic Disease Management (CDM) plan, where dietetic services are subsidized by Medicare.
