Low-carbohydrate and high-fat intakes were observed at baseline among most participants with poorly controlled T2DM at our primary care clinic, despite the exclusion of patients following low-carbohydrate dietary programs such as the Atkins and South Beach diets. The lower-carbohydrate intake appeared to reflect the usual dietary pattern for these patients and was associated with a high saturated fat intake and a low dietary fiber intake. Our observations may be representative of many other patients with T2DM, and perhaps of a trend in the wake of the low-carbohydrate diets. Such a diet likely has cardiovascular implications for patients with T2DM, obesity, hypertension, and hyperlipidemia. Although many researchers are advocating this low-carbohydrate approach to diabetic management [28
], more research is needed to determine the effect of this dietary recommendation on other macronutrients such as saturated fat and fiber.
We found saturated fat intake to be more than twice that of the American Heart Association recommendation [30
]. We speculate that, when reducing carbohydrate intake to control weight and hyperglycemia, participants appeared to have replaced the energy they previously got from carbohydrate with energy from fat. Further, participants did not choose to replace carbohydrates with the monounsaturated or polyunsaturated fats that have been shown to be cardioprotective. The ADA recommends a diet with <7% saturated fat content for people with diabetes [11
]. It is well understood that saturated fat is one of the main factors contributing to elevation of low-density lipoprotein cholesterol, which can increase risk of cardiovascular disease and overall inflammation [33
Also against current recommendations, dietary fiber and, in particular, soluble fiber intakes were found lacking among study participants. For people without diabetes, total dietary fiber intake is recommended to be 14 g/1000 kcal each day, including soluble and insoluble fibers [34
]; the recommended intake is higher for individuals with diabetes [11
]. Dietary fiber intake is inversely associated with levels of C-reactive protein [35
], a marker of inflammation predicting future coronary heart disease (CHD) [36
]. Soluble fiber is also of benefit in lowering low-density lipoprotein cholesterol and is mainly found in whole grains such as barley and oats and in legumes, fruits, vegetables, nuts, and ground flax seeds. Insoluble fiber promotes normal bowel function, prevents constipation, and can be found in whole-grain bread, whole-grain breakfast cereals, wheat bran, seeds, and many vegetables. In addition, whole-grain carbohydrate foods (containing soluble and insoluble fibers) are a nutritious part of the diet, with vitamins and minerals essential to many physiologic functions.
Contrary to the ongoing popular trends to lower total carbohydrate for weight loss, it may prove to be more effective and better for overall health to distinguish between types of carbohydrate rather than to focus on total quantity. The association of GI, carbohydrate intake, and BMI was investigated by our group using data from 563 healthy study participants in central Massachusetts [23
]. BMI was found to be positively associated with the GI, a measurement of the glycemic response associated with the ingestion of different types of carbohydrate, but not with daily carbohydrate intake, percentage of energy from carbohydrate, or GL. If patients are attempting to lose weight, a low total carbohydrate intake goes against this finding. Choosing whole-grain carbohydrates rather than avoiding carbohydrate foods may be a wiser approach.
Dietary composition observed in the present study of people with diabetes diverges from the NHANES (U.S. general population) data. In a study of nutrient intake and eating frequency using data from the NHANES III (1988–1994), carbohydrate intake for U.S. adults was 44.9–51.1% of daily energy intake in kilocalories, whereas fat accounted for 32.7–36.7% of energy intake [42
For historical comparison with the same geographic area as our present study, we draw from two of our previous studies in the mid-1990s [23
], for which dietary data were collected using the same diet assessment methodology. Dietary composition was approximately 45% of energy from carbohydrate, 36% from fat, and 19% from protein (not far different from that of the NHANES covering the same time period). The study groups consisted of a predominantly overweight and hyperlipidemic population without diabetes of any type.
Our data agreed with the findings that patients with T2DM tend to have a lower carbohydrate intake than that of the general population. Eeley et al. [44
] in 1996 reported a consumption of 43% of energy from carbohydrate in 132 adults with T2DM in the United Kingdom [44
]. Ten years later, in 2006, our study population with T2DM consumed 36% of energy from carbohydrate, a significant decrease. A sampling of other observational studies dating back to 1980 indicates that the general population consumes, on average, between 40% and 50% carbohydrate content [45
]. We have listed dietary composition in comparison with other populations and studies in .
Summary of dietary composition from selected literature
There are several possible explanations for the dietary differences between our previous studies in patients without T2DM and the present study. First, the present study was conducted between 2005 and 2006, when low-carbohydrate diets and food options are not unusual [50
]. According to consumer research in 2005 [51
], 40% of U.S. adults reported that they had reduced their carbohydrate intake. Second, approximately 80% of the subjects from our present study were obese, recognized they had problems with weight, and had tried to lose ≥10 lb in the previous year, possibly through an even stricter reduction of total dietary carbohydrate. Although the participants stated that they were not currently following a low-carbohydrate diet, this may have been in comparison with previous experience, and they may have retained many of the core components of the current popular trend. Third, our participants were also battling hyperglycemia, and the low-carbohydrate options that are readily available from the food supply offer an approach to glucose management.
Of the three macronutrients (carbohydrate, protein, and fat), carbohydrate intake has the greatest influence on blood glucose, although the overall balance of micro- and macro-nutrients has implications for diabetic complications. When diagnosed with T2DM, patients are generally instructed to carefully monitor their intake of carbohydrate and to distribute carbohydrate intake evenly throughout the day. Despite ADA recommendations, patients may find simple reduction of total carbohydrate easier than monitoring via the exchange system or distinguishing between types of carbohydrate.
The prevalence of obesity was higher in our sample (77.5%) compared with data from the NHANES 1999–2002 that recorded a 54.8% prevalence of obesity among adults diagnosed with diabetes [9
]. Popular weight-loss regimens also have shifted since the NHANES study. Clearly, the low-carbohydrate diet for weight loss has become popular in the United States over the past several years and, although currently waning, has retained many of its central features [13
In our sample, it is alarming to note that carbohydrate intake has been replaced with fat, especially saturated fat, and has also resulted in a low-fiber diet. It is widely accepted that diets high in saturated fat increase the risk of CHD [52
], and there is a fairly broad-based consensus on the role of dietary fat (especially saturated fatty acids) in hyperlipidemia and on the role of hyperlipidemia in CHD. Patients with diabetes are particularly vulnerable to CHD. There is no doubt that the diabetic diet is a complex one (and time consuming for the busy clinician to devote time to instruction), yet the effect of reduction of total carbohydrate on other dietary factors, such as increased saturated fat and decreased dietary fiber, must be moderated by additional instruction to balance the diet toward one that is also heart healthy.
Limitations of the study include small sample size, which limits generalizability, and the fact that this analysis was a case-series rather than a case-control design. This study is a pilot trial designed to test the feasibility and efficacy of a low-GI diet in comparison with standard ADA recommendations; as such, it is not designed to compare nutrient intake between subjects with diabetes and subjects without diabetes. However, we did compare our data with the national sample (NHANES), two sample studies from the local population, one from subjects with T2DM in 1996, and a sample of other studies. We believe that our analysis of the study provides an important cautionary tale for clinicians and health professionals who treat T2DM. Additional limitations are possible inaccuracies in participants’ reported diet composition on the 7DDR [55
] questionnaire. Although the 7DDR is fairly accurate in assessing total and saturated fat intakes, trans-fatty acid intake cannot be obtained. Strengths of the study include detailed information obtained about diet, blood lipids, comorbidities, and medication use.