Carbohydrate, Fat, and Protein: What Do We Know about the Macronutrient Composition of the Diet following Bariatric Surgery?

| May 5, 2008

by Liz Goldenberg, MPH, RD, CDN

As practitioners in the field of bariatric surgery, our aim is to assist patients in achieving their goals of improved health and quality of life by accomplishing weight loss and decreasing the risk of obesity-associated comorbidities. While it is agreed that weight loss results from higher calorie expenditure than intake, it has been debated whether where the calories come from matter. In other words, does the relative contribution of macronutrients to the diet after weight loss surgery impact weight loss?

The Macronutrients: Dietary Role, Body Requirements, and Weight Loss Considerations
Protein. We will first overview the macronutrients, beginning with protein. This important nutrient provides 4kcal/g and supplies amino acids for synthesis of crucial body substances, including enzymes, hormones, and immune factors. These function in wound healing and maintaining visceral protein while decreasing loss of lean body mass. Many believe that dietary protein also functions to increase satiety, thus aiding weight loss.1,2 One way in which this might work is by taking into account the relative density of high protein foods. While high carbohydrate foods like fruits and vegetables have a high water content, and starches such as potatoes, bread, crackers, and pretzels require a small amount of chewing, animal proteins such as poultry, beef, fish, and pork are heavier and require more mastication before swallowing. Perhaps these denser foods stay in the stomach longer (and even longer in the post-surgery restricted stomach), are slower to empty from the stomach, and lead to a prolonged sense of satiety. Additionally, high protein diets have been reported to induce a greater thermic effect since utilizing protein for energy is metabolically more costly.2 Very high protein diets are resultantly low in carbohydrate. Low carbohydrate diets may aide weight loss by other mechanisms, which will be addressed later in this article.

Many programs recommend a range of 60g to 80g daily or 1.0g to 1.5g of protein/kg ideal body weight (IBW), although exact recommendations have yet to be agreed upon. The use of 1.5g of protein/kg IBW/day beyond the early post-surgical phase is probably only necessary for patients with complications. However, since patients do not seem to be meeting even basic protein requirements of 0.8g/kg [see Table 1 for protein Dietary Reference Intakes (DRI)] early on, liquid protein supplements are commonly recommended.3,4,5 Supplements derived from complete protein sources like milk, egg, or soy are usually preferable to those that merely provide individual amino acids or are collagen-based and may lack tryptophan.1,6

It is important to note here that absolute protein requirements are higher for malabsorptive operations such as duodenal switch (DS) and biliopancreatic diversion (BPD). Scopinaro showed daily intestinal nitrogen losses to be five times greater after BPD and recommends an average daily protein intake of 90g to prevent malnutrition.7 These constitute the minority of operations performed in this country, and this paper focuses on the operations that are considered mostly restrictive, such as gastric band, gastric bypass, and sleeve gastrectomy, except where otherwise noted.

Carbohydrate. The main nutritional function of carbohydrate is to provide energy to cells in the body, especially the brain. Like protein, this macronutrient provides 4kcal/g (see Table 1 for carbohydrate DRI). Diets that provide less than approximately 100g of carbohydrate daily (thus high protein diets) induce ketosis. Ketosis is believed to reduce basal insulin levels, promote lipolysis, reduce lipogenesis, and suppress appetite.2 Since our brains are carbohydrate-dependent organs, ketosis may impair judgment or have other negative effects on the central nervous system.

The carbohydrate content of the diet is believed to be relevant in weight regulation because carbohydrates can easily contribute to excess energy intake. Dietary fiber glycemic index (GI) and glycemic load (GL) each may play a role in energy regulation. High-fiber foods are usually lower in calorie density, may help to increase feelings of fullness by combining with water to form a viscous gel, and may slow gastrointestinal transit time, thereby increasing blood sugar more gradually. High-fiber foods typically have a low GI. GI reflects carbohydrate quality while GL takes into account both GI and total carbohydrate content. Choosing a diet consisting of low GI foods may perhaps increase satiety and prevent rapid spikes and declines in blood glucose and counter-regulatory hormones.9

A special consideration with weight loss surgery is that a reduced-volume stomach does not limit fluid intake to the same degree that it restricts solid food. Intake of high carbohydrate beverages, such as non-diet soda or juice, or even “liquid-like” foods, such as pudding and ice cream, are easy ways to take in a large amount of carbohydrate calories while avoiding satiety (assuming that dumping is not an issue).

Fat. Fats act as precursors in prostaglandin production, are necessary to prevent essential fatty acid deficiency, and help to absorb the fat-soluble vitamins A, D, E, and K. Dietary fats are broken into groups of saturated, monounsaturated, polyunsaturated, and the artificially-derived trans fats. Each gram of fat provides 9kcal (see Table 1 for fat DRI). Considering the high palatability of fatty foods, and their nutrient density of more than double that of protein and carbohydrate, it seems rational that following a high fat diet might lead to weight gain.2

Should Diet Composition Differ for Those Trying to Lose Weight With or Without Surgery?
An important question that we need to ask is whether diet recommendations for weight loss and health promotion should differ among the obese versus the obese that undergo weight loss surgery. Based on the available data, there does not appear to be any evidence that the guidelines should be unique for these different populations looking to lose weight. While we know more about weight loss surgery nutrition each year, there need to be more studies. Currently, most weight loss professionals agree on the “tool” concept of bariatric surgery, whereby those undergoing surgery should aim to eat a healthy diet and exercise,10 while benefiting from the assistance that surgery provides. Assistance is in the form of limiting portion sizes, and in some instances providing malabsorption, negative feedback (as in dumping or vomiting), and depressing appetite. In other words, as might be overheard in a nutritionist’s office, the idea is to try to choose to eat a baked potato more often than French fries, not to count on losing weight by being full after a small order of fries instead of the super-sized version.

But what is a healthy weight loss diet?
We have another question to ask. Do we all agree on what healthy means? Although a favorite expression of dietitians like this writer, healthy diet does not have a clear definition. If we all agreed on a definition, it would be the one that consistently resulted in significant, long-term weight loss, was easy to follow, and did not seem to have any negative health consequences (such as deleterious cardiovascular or cognitive effects). Probably all healthcare practitioners would be on board if this were the case. Judging by the array of popular diets recommended by health experts, there does not seem to be such a plan out there. Additionally, many authorities in the field will even try to avoid the word “diet” altogether, and instead emphasize behavior and lifestyle.

The baked potato versus French fries example is probably one on which we all can agree. Also, most would accept the choice of a fresh orange versus a can of orange flavored soda. Choosing the potato and the orange would go along with the “traditional” diet plan, backed by groups such as the American Heart Association, American Cancer Society, National Institutes of Health, and the American Dietetic Association, which promotes a “healthy” diet that is low in saturated fats and simple sugars, while high in fresh fruits, vegetables, and whole grains. This is a low-fat, high-carbohydrate plan of 55 percent of calories from carbohydrate, 30 percent from fat (and no more than 10 percent from saturated fat) and 15 percent from protein. This is in line with the much broader Acceptable Macronutrient Distribution Range (AMDR) promoted by the Institute of Medicine: 45 to 65 percent of calories from carbohydrates, 20 to 35 percent from fat, and 10 to 35 percent from protein (see Table 1). These guidelines aim to decrease the risk of developing chronic diseases, such as cancer, diabetes, cardiovascular disease, and obesity.2, 11 It seems reasonable to assume that these guidelines would best serve our patient population as well, but there is a lack of studies that specifically look at this.

Here again is another place to point out an exception for more malabsorptive surgeries. As mentioned above, due to malabsorption, BPD and DS protein requirements are higher. Fat is also significantly malabsorbed, and thus eating more fat may aid weight loss (but also will lead to more frequent and/or loose stool). Therefore, dietary recommendations for these operations should be unique.12

Popular Diets and their Macronutrient Composition: An Overview
High protein/very low carbohydrate diets. The name Dr. Atkins is synonymous with the all-you-can-eat meat and no-potatoes plan, which ignores portion control and typically results in a high percentage of calories from fat.

Low carbohydrate diets. These diets have a more moderate carbohydrate allowance. Both The Zone (40%–30%–30% carbohydrate, fat, and protein respectively) and Dr. Agatston’s South Beach diet might be placed in this category. The low GI diet encourages avoidance of foods with a high glycemic index; this diet probably fits best into the low carbohydrate category.

Very low fat diets. These diets are often also vegetarian, such as Dr. Ornish’s plan for no more than 10 percent of calories from fat.
High carbohydrate diets. The more traditional plans based on national dietary guidelines (as mentioned above) would fall into this category. Other well known programs include the LEARN (lifestyle, exercise, attitudes, relationships, and nutrition) plan and the Food Guide Pyramid.

Others. There are other popular diets that do not fit easily into the above categories as they do not emphasize macronutrient ratios. Weight Watchers instead restricts calories via portion control. The Mediterranean style of eating underscores type or quality of fat and carbohydrate and not their relative amounts; this diet has become popular for its link to heart health. Of course there are many more diets out there; the aforementioned are but a partial listing.

How do the diets compare?
Four papers from last year reviewed the association between diet composition and weight loss.7, 9, 11,13 The majority of evidence seems to support an inverse relationship between carbohydrate intake and body mass index (BMI), although a high protein/low carbohydrate diet plan probably leads to more weight loss in the short term. Studies looking at glycemic index are not conclusive. Some do not show evidence of reduced BMI, but do show cardiovascular benefits, probably because of their emphasis on fruits, vegetables, and whole grains. High glycemic load does seem to be associated with lower BMI.13,14,15

Interestingly, the majority of data supports the notion that factors other than macronutrient composition are responsible for weight loss success. In other words, all tweaking of proteins, fats, and carbohydrates aside, any diet will do, as long as someone can stick to it.2, 16, 17 Only rarely do diet trials go beyond 6 to 12 months; cost is a significant factor. Increased dietary adherence seems to be consistently associated with greater weight loss, but overall adherence rates are lower than one would hope for in otherwise well-designed studies (at least one study paid participants for their continued involvement). Subjects cite inadequate weight loss and difficulty following the diets as reasons for dropping out. There may be an association between higher discontinuation rates for the stricter diet programs, such as the very low carbohydrate Atkins diet and the very low fat Ornish diet.17 In two trials each with four groups of subjects who followed four dissimilar diets, the differences between the diets started to become less apparent after only two months.17,18 Again, more studies need to be done as there are many limitations to the data at this point.

The National Weight Control Registry, a listing that maintains information on people who have successfully lost weight and maintained weight loss, shows us that trends among dieters change along with the popular diets of the time. This seems supportive of the notion that substantial weight loss is possible over a wide range of diet compositions.9
Another factor that is closely linked to success is the human factor. Programs that provide more support and follow-up seem to be more effective.16,17

Does type of fat matter with regard to weight loss?
Strictly speaking, an equal number of fat grams derived from cheeseburgers and walnuts will provide the same number of calories. While it appears that the type of fat affects health, specifically cardiovascular status, it is not as clear if the fat source matters when it comes to weight loss. Data from both the often-cited Mediterranean Diet and The Nurses’ Health Study (NHS) are two examples that help support the theory that macronutrient composition, rather than merely the caloric content of fat, is relevant. The eight-year follow-up of nurses from the NHS showed that total percentage of calories from fat was positively associated with weight gain. However, diets higher in saturated and trans fats (vs. monounsaturated and polyunsaturated fats) were associated with greater weight gain.2, 19

The fat debate is by no means resolved; there needs to be more research to tease out the correlation between type of fat and body weight.
As described above, BPD and DS patients can achieve more weight loss by liberalizing fat intake. However, a concern for dietitians working with this population is whether we need to pay attention to the type of fat. There are no studies that this writer is aware of that look at whether (for another example) peanut butter is a better choice of spread than traditional butter. While it seems wise to choose monounsaturated and polyunsaturated fats over saturated and trans fats for their link to cardiovascular disease, there is no data on the ramifications of these choices in this unique group of malabsorbers.

Nonalcoholic fatty liver disease (NAFLD)
There is some data that macronutrient composition matters when it comes to specific health conditions. One such condition is NAFLD. Benjaminov, et al., found that four weeks of a very low carbohydrate diet (54+22g/day) led to a reduction in liver fat in preoperative obese patients. The left lobe of the liver was reduced enough to facilitate the weight loss operations. Authors also found a significant decrease in HDL but no change in triglycerides or cholesterol.20 Once again, the results of this small study (n=14) only serve to reinforce the short-term effects of a very low carbohydrate diet.

What are our patients eating after weight loss surgery?
In the beginning, they are not eating a whole lot. Tables 2, Table 3, Table 4, Table 5, Table 6, and Table 7 show the macronutrient composition of the diets of postoperative gastric bypass patients from six different studies.4, 5, 21, 22, 23, 24 When percentages do not total 100, the difference is from alcohol. To help interpret the comparable weight of each study, the tables also show the number of subjects and the method of dietary
analysis used.

The studies detailed in Tables 2 through 7 are listed in order of publication from oldest to newest. With the exception of the Coughlin paper from 1983 (one of the earliest papers to report on gastric bypass nutrient intake), they are all fairly recent studies, from 2002 to 2006. The number of subjects per study went from as few as 25 to as many as 93. Diet recall was the analysis method most frequently used. All of these studies agree that calorie intake increases over the first year, and that largest proportion of the post-gastric bypass surgery diet comes from carbohydrates (and the smallest from protein). Twelve-month calorie intakes varied widely in these papers, from as few as 866 daily to as many as 1,465. Wardé-Kamar’s paper, the only one to look at data from patients who were more than one year past their operations, not surprisingly reported the highest daily calorie intake, at 1,733.

There are a small number of studies which specifically report on the macronutrient content of post-surgery diets and try to determine whether diet composition matters with regard to weight loss.

In the Bobbioni study22 (Table 3) of 50 women who underwent RYGB, patients were advised to consume 60g of protein/day, and 1,000kcals/day during the first month, 1,200 kcals/day from the first to fourth month, and 1,400 kcals/day from the fourth month of surgery on. After analyzing the breakdown of the patients’ intakes, authors concluded that diet composition did not influence the extent of weight reduction—instead energy intake alone affected weight loss.

Thomas25 gave questionnaires to 38 gastric bypass patients in the period of three months to two and one-half years following surgery. The findings were surprising in that patients tended to select low-fat foods over the higher fat ones more often, even though the low-fat foods were more likely to give them symptoms of intolerance. Olbers24 (Table 6) also found gastric bypass patients tended to avoid fatty foods, but in contrast to the Thomas study, their patients did report not feeling well after eating the high fat items. Researchers went on to conclude that the lower fat composition of the diet following gastric bypass is responsible for greater weight loss as compared with purely restrictive procedures24 (Table 7). Only a very small number of patients (4/93) in a third study reported fat intolerance; however, this was not associated with a greater percentage of excess weight loss5 (Table 4).

Immediately following surgery, patients are often consuming less than 50g of carbohydrate daily, and thus may be in ketosis. Is this desirable? It may act as a key motivator by helping to jump-start their weight loss. At least for the short term it does not appear to be harmful. However, there may be side effects if this is prolonged. Rapid weight loss has been linked to both hepatic disease and kidney stones, and when associated with frequent vomiting, thiamine deficiency as well.26 Even at one year out, many patients fall below the 100g level of carbohydrate intake.

This paper discusses the debate over the optimal diet composition to accomplish and maintain weight loss after bariatric surgery. The complexity of our diets, the limitations of experimental versus observational study design, the metabolic differences between lean, obese, and normal weight subjects, and of course the costs and difficulties associated with accurately measuring both nutrient intake and energy expenditure, are among the many reasons that ensure the debate will continue.9 Hopefully this piece has served to summarize the available data as it relates to dietary macronutrients, weight loss, and weight loss surgery. There is likely no one diet prescription that will work well for all; indeed, data from the National Weight Control Registry support this.

I will propose the following take home messages: Weight loss success is probably more easily achieved for those that follow up with their healthcare providers, continue to expend energy by participating in an exercise program,10 and find a nutritional plan that they are able to commit to for a long time, or ideally, a lifetime. Lastly, more research needs to be done with regard to the most effective diet composition for weight loss surgery patients.


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Category: Nutritional Considerations in the Bariatric Patient, Past Articles

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