strategie nutrizionali per migliorare il glucosio post-prandiale

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Nuts, Olive Oil, and Fish Oil

Nuts, when consumed with a meal, will significantly reduce the post-prandial glucose excursion by slowing digestion. Recent studies show that almonds, pistachios, or peanuts, when eaten along with high glycemic index carbohydrates such as white bread or mashed potatoes, will reduce the post-prandial glucose area under the curve by approximately 30% to 50% (28) (Fig. 4). Importantly, nuts also decrease meal-induced oxidative protein damage because they lower post-prandial oxidative stress and additionally provide antioxidants (29 D. Jenkins, C. Kendall and A. Josse et al., Almonds decrease post-prandial glycemia, insulinemia, and oxidative damage in healthy individuals, J Nutr 136 (2006), pp. 2987–2992. View Record in Scopus | Cited By in Scopus (20)29).


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Figure 4. Almonds Reduce Post-Prandial Glucose
The post-prandial increase in the area under the curve for glucose was reduced by 58% when 90 g of almonds were added to a high glycemic index meal (p = 0.009). Data from Josse et al. (28 A. Josse, C. Kendall, L. Augustin, P. Ellis and D. Jenkins, Almonds and post-prandial glycemia—a dose-response study, Metabolism 56 (2007), pp. 400–404. Abstract | Article | PDF (239 K) | View Record in Scopus | Cited By in Scopus (13)28).


A recent trial randomized 772 subjects at high risk for CAD to a low-fat diet or a Mediterranean-style diet supplemented with either walnuts (30 g/day) or virgin olive oil (1 l/week). This trial found that after 3 months the Mediterranean diets supplemented with either nuts or olive oil produced clinically significant reductions in systolic blood pressure, fasting glucose, and inflammatory biomarkers compared with the low-fat diet (1).
Epidemiologic studies consistently indicate that consumption of nuts at least 5 times per week will reduce CAD and diabetes risks by 20% to 50% (29). Tree nuts are comprised predominantly of monounsaturated fats and are a rich source of antioxidants, fiber, phytosterols, magnesium, and folic acid, which might beneficially influence CV risk. Replacing refined carbohydrates with monounsaturated fats (using nuts and/or olive oil) will reduce post-prandial hyperglycemia and hypertriglyceridemia, increase high-density lipoprotein, and decrease oxidative stress ([1] and [2]). One practical way to accomplish this is to substitute nuts (all of which have very low glycemic indexes) for the sugary and starchy snack foods that are staples in the American diet.
Fish oil (omega-3 fatty acids) lowers post-prandial triglyceride levels by 16% to 40% in a dose-dependent fashion, in part by upregulating lipoprotein lipase activity and accelerating the clearance of chylomicrons (30). Thus, some of the documented anti-inflammatory and cardioprotective activities of omega-3 fatty acids may be conferred in part by significant improvements in post-meal lipid levels (31).

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Vinegar

A mixture of vinegar and olive oil is the traditional salad dressing used in the Mediterranean diet. The consumption of vinegar with meals was used as a home remedy for diabetes before the advent of pharmacologic glucose-lowering therapy. Indeed modern studies indicate that vinegar significantly reduces post-meal glycemia, probably because acetic acid slows gastric emptying and thus delays carbohydrate absorption and improves satiety. Recent studies show that 1 to 2 tablespoons of vinegar, when added to a meal containing high-glycemic-index foods such as white bread or white rice, will both: 1) lower post-prandial glucose by 25% to 35% (Fig. 5), and 2) increase post-meal satiety by more than 2-fold (32). Thus the addition of vinegar to a standard meal can not only improve the meal-induced oxidant stress by blunting the post-prandial glucose excursion, but also can increase and prolong satiety, which should help to reduce food cravings and lower caloric intake over the subsequent 2 to 4 h. Finally, vinegar with olive oil is generally consumed with green leafy vegetables, which have superior nutrient-to-calorie ratios and very low glycemic indexes.


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Figure 5. Vinegar Reduces Post-Prandial Glucose
The addition of 2 tablespoons of vinegar to 2 slices of white bread significantly reduced the post-prandial glucose increase. Data from Östman et al. (32).

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High-Biological-Quality Protein

Protein is an important component of an anti-inflammatory, cardioprotective diet. Unfortunately, the favored protein sources in the modern diet, such as ground beef, sausage, bacon, and cheese, are high in both calories and saturated fats and tend to worsen post-prandial dysmetabolism ([3] and [11]). In contrast, lean protein of high biological value will both reduce post-meal glucose excursion and improve satiety. In a study of healthy individuals, the addition of whey protein to a pure glucose drink lowered the post-prandial blood glucose area under the curve by 56%, and increased the insulin response by 60% (33) (Fig. 6). Additionally, dietary protein has a thermogenic effect whereby it increases the basal metabolic rate, which is not the case with ingested carbohydrates (25). Thus, protein of high biological quality such as egg whites, fish, game meat (and other very lean red meats), skinless poultry breast meat, and whey protein (or other nonfat dairy protein) when eaten with meals will dampen down post-prandial inflammation and can help prevent obesity (25).


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Figure 6. Whey Protein Reduces Post-Prandial Glucose
Increases in blood glucose after either a glucose drink or the same glucose drink mixed with whey protein. Whey protein reduced the area under the curve for blood glucose by 56% (p < 0.05). Data from Nilsson et al. (33).

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Calorie Restriction and Weight Loss

Weight loss of 5% to 10% or more, particularly when accompanied by decreased abdominal adiposity, lowers post-prandial glucose and reduces the risk of new diabetes (25). Although weight loss can be achieved by any dietary modification that reduces calorie intake, strategies that restrict both processed carbohydrates and unhealthy fats (saturated and trans fats) improve post-prandial dysmetabolism, oxidative stress, and inflammation more effectively than other approaches ([1], [2] and [25]).
The degree of post-prandial dysmetabolism is closely related to calorie intake. On the extreme end of the spectrum, fasting completely eliminates post-prandial increases in glucose and triglycerides and the ensuing oxidant stress and inflammation. A reduction in calories by approximately 30% below the intake on an ad libitum diet has been shown to improve health and longevity in animal models (34). A similar degree of calorie restriction in humans has been achieved by diets low in processed foods and high in vegetables, fruits, nuts, low-fat dairy, egg whites, soy protein, whole wheat, and lean meat that provides >100% of the daily value for all of the essential nutrients ([34] and [35]). This diet was associated with improvements in oxidative stress, inflammation, glucose, insulin sensitivity, blood pressure, lipids, and cardiac function ([34] and [35]). Although the ideal caloric intake for optimal health and longevity is yet to be determined in humans, the avoidance of energy-dense processed foods is a logical first step toward the reduction of excess calories.
Light to Moderate Alcohol Consumption

An extensive body of data shows concordant J-shaped associations between alcohol intake and a variety of adverse health outcomes including CAD, diabetes, stroke, dementia, and all-cause mortality (36). Light to moderate alcohol consumption (0.5 to 1 drink daily for women, and 1 to 2 drinks daily for men) is associated with cardioprotective benefits, whereas increasingly excessive consumption results in proportional worsening of outcomes. Although alcohol increases high-density lipoprotein in a dose-dependent fashion, the effects on glucose homeostasis are nonlinear, conferring benefits at lower doses and harm at higher doses (36). Randomized placebo-controlled trials in healthy nondiabetic individuals showed that 1 to 2 drinks immediately before a meal will significantly lower post-prandial glucose and insulin levels (37) (Fig. 7). Tellingly, the interaction between alcohol intake and post-prandial glucose follows the same J-shaped relationship that is seen between alcohol and systemic inflammation, as well as alcohol and adverse CV events (36 J. O’Keefe, K. Bybee and C. Lavie, Alcohol: the razor-sharp double-edged sword, J Am Coll Cardiol 50 (2007), pp. 1009–1014. Article | PDF (457 K) 36).


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Figure 7. Alcohol Reduces Post-Prandial Glucose
In this group of healthy individuals, 20 g alcohol (approximately 1.5 drinks) in various beverages reduced postmeal glucose by up to 38%. Data from Brand-Miller et al. (37).

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Consuming a light to moderate amount of alcohol, like exercise, will increase insulin sensitivity and glucose metabolism for the ensuing 12 to 24 h (36). Indeed, daily low-dose alcohol is associated with better health than less frequent consumption (36). Regular light to moderate alcohol intake with the evening meal is traditional in many of the cultures with exceptional health and longevity.

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Exercise

Sedentary behavior worsens insulin resistance and magnifies the post-prandial excursions of glucose and triglycerides. In contrast, exercise improves insulin sensitivity predominantly in the skeletal muscles, and acutely lowers glucose and triglyceride levels in a dose-dependent fashion. A single bout of 90 min of moderate-intensity exercise (walking briskly) within 2 h before or after a meal has been shown to lower post-prandial triglycerides and glucose levels by about 50% ([3] and [38]). A recent study using continuous objective activity monitoring in 173 nondiabetic individuals found that cumulative daily physical activity, even light-intensity activity, was associated in a dose-dependent fashion with lower 2-h post-challenge glucose levels (but not fasting glucose levels) (Fig. 8). The same study showed that cumulative sedentary time was associated with higher 2-h glucose levels (39 G. Healy, D. Dunstan and J. Salmon et al., Objectively measured light-intensity physical activity is independently associated with 2-h plasma glucose, Diabetes Care 30 (2007), pp. 1384–1389. View Record in Scopus | Cited By in Scopus (26)39).


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Figure 8. Daily Activity Reduces Post-Prandial Glucose
Cumulative daily light-intensity physical activity was inversely associated with post-prandial glucose levels. Data from Healy et al. (39).

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Physical activity improves inflammation directly by lowering post-prandial glucose, and indirectly by reducing excess abdominal fat (39). Studies show that the body will preferentially mobilize and oxidize fatty acids from adipose tissue during exercise after a low glycemic index meal rather than a high glycemic index meal (40). Thus over time lower glycemic index diets combined with regular exercise may be useful for optimizing loss of excess visceral fat ([10], [25] and 40 E. Stevenson, C. Williams, L. Mash, B. Phillips and M. Nute, Influence of high-carbohydrate mixed meals with different glycemic indexes on substrate utilization during subsequent exercise in women, Am J Nutr 84 (2006), pp. 354–360. View Record in Scopus | Cited By in Scopus (15)[40]).

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Summary and Recommendations

The modern calorie-dense, nutrient-poor diet of processed foods, especially when combined with a sedentary lifestyle and abdominal obesity, produces exaggerated post-prandial increases in glucose and lipids, which leads to inflammation and atherosclerosis. In contrast, a diet high in minimally processed, high-fiber, plant-based foods such as low glycemic index vegetables and fruits, whole grains, legumes, and nuts will markedly blunt the post-meal increase in glucose and triglycerides. Additionally, lean protein, fish oil, calorie restriction (ideally induced via avoidance of processed foods and excessive portion sizes), weight loss, vinegar, cinnamon, tea (41 J.A. Byrans, P.A. Judd and P.R. Ellis, The effect of consuming instant black tea on postprandial plasma glucose and insulin concentrations in healthy humans, J Am Coll Nutr 26 (2007), pp. 471–477.41), and light to moderate alcohol intake and physical activity positively impact post-prandial dysmetabolism (Table 1).


Table 1. Steps to Improve Post-Prandial Glucose and Triglycerides

1 Choose high-fiber, low glycemic index carbohydrates such as whole grains, legumes, and vegetables and fruits.
2 Eat lean protein at all 3 meals.
3 Consume nuts on a daily basis, about 1 handful (with a closed fist). Eat with vegetables, berries or other fruits, or grains.
4 Eat a salad of leafy greens dressed with vinegar and virgin olive oil on a daily basis.
5 Avoid highly processed foods and drinks, especially those containing sugar, high-fructose corn syrup, white flour, or trans fats.
6 Keep serving sizes modest.
7 Avoid being overweight or obese; maintain a waist circumference less than one-half of height in inches.
8 Obtain 30 min or more of daily physical activity of at least moderate intensity.
9 Consider consuming 1 alcoholic drink before or with the evening meal (for those without a history of substance abuse).

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Acknowledgment

The authors thank Lori J. Wilson for her assistance with preparation of the manuscript and figures.

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