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High-Protein Diets Called Most Helpful for Weight Control
10/23/2006
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Zone and Atkins-style diets found superior to common high-carb diets in two small clinical studies; supplemental omega-3s amplify benefits
by Craig Weatherby


New clinical findings from Europe give popular high-protein eating plans two big wins in the ongoing diet wars.

A small pilot trial from Italy credits the high-protein, low-carb, fish-and-vegetable favoring Zone diet with cutting body fat and improving a range of health measures.

Key Points
  • Italian trial finds Zone diet cuts body fat and improves general health markers more than a conventional, higher-carb diet.
  • Benefits of Zone diet were enhanced by omega-3 fish oil capsules, versus olive oil placebo capsules.
  • British trial finds that high-protein diets beat high-carb diets when it comes to suppressing appetite in men and mice.
Meanwhile, a small pilot clinical trial (and accompanying animal study) from Britain boosts the anti-obesity prospects of high-protein, low-carb Atkins-style diets in general.

Let’s take a closer look at these enlightening (pardon the pun) results.

Atkins and the Zone: a quick review
Dr. Atkins’ bestsellers of the 1980's defied the conventional wisdom that low-fat, high-carb diets were best for weight control.

But his low-carb, high-protein suffered some well-deserved slings and arrows for a failure to distinguish between healthful and unhealthful sources of protein.

Under the original Atkins approach, a saturated-fat-laden slab of bacon was seen as no different than a leaner, omega-3-rich salmon fillet. His approach rested entirely on the idea (unproven at the time) that protein is more satiating than carbohydrates, and he was unconcerned about the source.

Barry Sears, Ph.D., whose book The Zone created the “Zone diet” craze of the late 1990’s, arrived at support for high-protein diets from a different, more scientifically sophisticated angle.

Unlike the Atkins plan, Sears’ diet made distinctions between healthful fats (omega-3s and monounsaturates) and fats Americans consume to unhealthful excess (omega-6s and saturated fats, which are not inherently unhealthful).

The Zone diet plan also distinguished between healthful carbs (vegetables, fruits, whole grains) and unhealthful carbs (e.g., white bread, potato chips, pastries).

Dr. Sears proposed that the key to weight control was to adjust the diet in three key ways, to produce specific metabolic effects:
  1. Consume the three essential macronutrients in a particular proportion--40 percent carbohydrates, 30 percent protein, and 30 percent fat--to satiate appetite and stabilize blood sugar levels.
  2. Favor low-glycemic carbs (vegetables, whole grains) to prevent large swings in blood sugar levels, which can result in storage of calories as hard-to-lose body fat.
  3. Favor fish as a protein source because its omega-3 fatty acids exert desirable influences over the body’s ephemeral, hormone-like messenger chemicals called autocoids (e.g., eicosanoids, prostaglandins, and cytokines), which have profound effects on human metabolism, including fat-burning and inflammation.

    • Group Z ate a Zone-type diet, consisting of 40 percent carbohydrates, 30 percent protein, and 30 percent fat and featuring fish, vegetables, and fruit.
    • Group N ate the diet recommended by the Italian National Research Institute for Nutrition and Foods, which consists of 55 percent carbohydrate, 15 percent protein and 30 percent fat) and features pasta, bread and meat.
    • Groups ZA and NA took placebo (olive oil) capsules from day 1 to day 35 and then switched to taking omega-3 fish oil capsules from day 36 to day 70.
    • Groups ZB and NB took omega-3 fish oil capsules from day 1 to day 35 and then switched to taking olive oil capsules from day 36 to day 70.
    • “The results suggest that some of these effects are owing almost exclusively to diet, particularly the Z [Zone] diet (body fat), while others, such as the mood state variations, are mainly owing to Omega-3 supplementation, whose effects are strengthened by the Zone diet.”
    • “Although all subjects presented a reduction in body fat owing to the controlled diet, the Z diet had a stronger effect, consistent with the… changes in blood parameters, i.e. [reductions in the] AA/EPA [ratio], LDL [cholesterol levels] and insulin [levels].”
    • “The [lower] AA/EPA ratio is considered a predictor of health status with respect to the above-mentioned diseases, as well as an index of well-being.”
    • “Our results show that the N [higher-carb, lower protein] diet can induce variations in some [health] parameters, but the Z [Zone] diet has a greater effect on the same parameters and this is increased by Omega-3 supplementation.
    • “An important example is the AA/EPA ratio: it is… [reduced] more strongly by the Z diet and is greatly decreased by the addition of [supplemental] Omega-3 [from fish oil].”
    • “…it can be inferred that the use of a diet with specific rules and with a 40-30-30 ratio of carbohydrates, lipids and proteins is more effective than traditional diets in modifying some blood parameters and reducing body fat. Supplementation of this diet with Omega-3 fatty acids provides further benefits...”
    • “The reduced carbohydrate and increased protein in the Z [Zone] diet are believed to have beneficial effects on type 2 diabetes, cardiovascular diseases and obesity, thus reducing the risk of cardiovascular diseases.”
    • “This [Zone] diet also results in reduction of hunger, insulin resistance and lower body weight, along with increased adipose tissue metabolism [fat-burning] and a low glycemic index.”
    • “Increased blood levels of GH and IGF-1 [human growth hormones] have also been described in subjects on low-carbohydrate diets and this effect is accompanied by a lower triglyceride level. On the other hand, it has been reported that a high dietary glycemic load from refined carbohydrates increases the risk of coronary heart diseases.”
    • “Omega-3 fatty acids have similar [beneficial] effects on lipid metabolism. They reduce triglycerides, have anti-inflammatory effects, reduce the insulin response to glucose, and reduce the risk of cardiovascular diseases and cancer. The effects of Omega-3 fatty acids are improved by aerobic exercise, which is also advisable for subjects whose diet involves a high protein intake.”
    • “Supplementation with Omega-3 seems to be linked to an increase of vigor and a decrease of negative factors such as anger, anxiety and depression. This correlation was only present in subjects on the Z [Zone] diet. These results confirm the influence of Omega-3 on the central nervous system… They are also in line with the suggested action of these compounds on dementia, depression and mood disorders, in which they may act as mood stabilizers.”

  4. And research results from Italy suggest that Dr. Sears was not, as they say, just whistling Dixie.
Zone-type diet cuts body fat more than Italy’s official diet plan
    Last month, we reported on the results of a small pilot trial at Italy’s University of Siena, which indicated that omega-3s enhance fundamental aspects of brain function (see “Omega-3s Seen Boosting Performance of Healthy Young Brains”).
      In another phase of their trial, designed to test the health effects of the Zone diet versus a higher-carb, traditional-style Italian diet, the Siena team divided 33 healthy men and women (ranging in age from 22 to 51) into two groups (Fontani G et al 2005).
        Each of two groups--Z (Zone) and N--was assigned a different diet for 70 days:
          Each group (Z and N) was divided into two subgroups: A and B.
            (The olive oil and fish oil capsules were made identical in appearance and flavor to eliminate any bias.)
              In the end, both diets reduced participants’ body fat, but the group placed on the Zone diet enjoyed substantially bigger cuts in body fat, measured both as skin-fold thickness and the percentage of body weight occurring as fat.
                The Zone diet group also enjoyed the biggest improvements in every marker of health measured, including blood fat profiles (cholesterol and triglycerides), mood, and antioxidant defenses.
                  And while they were taking omega-3 fish oil, the participants in each group showed further improvements in every marker of health measured, above any improvements associated with either of the prescribed diets.
                    The only exception was that supplemental fish oil did not produce additional drops in body fat. However, this is not very surprising, since the addition of more fish oil to a 70-day-long Zone diet that was already rich in fish could be hard-pressed to produce significant additional body-composition improvements in just 35 days.
                      Here’s how the researchers expressed their findings. The AA (arachidonic acid) referred to is a pro-inflammatory omega-6 essential fatty acid, while EPA is one of the two key omega-3 fatty acids in fish oil, which the Italians used as a marker for omega-3 levels in the participants’ cells (we added clarifying text in [brackets]):
                        It is also worth quoting some of the Siena team’s observations concerning prior studies on the Zone diet and omega-3s as they relate to the positive results of the new clinical trial.
                          Note: the term “glycemic load” refers to the rise in blood sugar produced by a food; so-called “high-glycemic” foods (bread, pastries, etc.) raise blood sugar quickly and sharply, with deleterious long-term health effects:
                            We couldn't have said it better. And recent results from Britain lend the various high-protein diet plans further support.
                              Atkins diet beats high-carb alternative at satisfying appetites
                                Last month, scientists at University College London (UCL) published findings that suggest high-protein diets are more effective than high-carb diets in fighting obesity, and that they do it by satisfying hunger more effectively.
                                  Just a year ago, we reported on the discovery of one satiety-promoting effect of dietary protein in rodents (see “More Support for Protein-rich, Salmon-centric Diets”).
                                    The UCL team wanted to see whether diets high in protein could speed satiety in humans via another mechanism: by stimulating release of an intestinal hormone called PYY, which is believed to send “I’m full” signals from the gut to the brain.
                                      Working under lead researcher Dr. Rachel Batterham, the UCL team recruited 10 healthy normal-weight men and 10 obese men, who were given one of three calorie-equivalent meals: high-protein, high-fat or high-carbohydrate. The scientists analyzed the volunteers’ blood after the meals.
                                        The high-protein diet resulted in the greatest reduction in hunger in both normal and obese participants and produced the largest increase in blood levels of PYY.
                                          Interestingly, the post-meal levels of PYY were lower in the obese subjects: a result suggesting that one reason for their weight problems might be deficiencies in their production of PYY in response to dietary protein.
                                            The UCL team then used genetically modified mice to prove that it really was the PYY that produced the satiating effect.
                                              They found that mice that lacked the PYY hormone ate more than regular mice and became obese. And when they administered PYY to the PYY-deficient mice their food intake decreased to normal levels, as did their weight.
                                                As the authors said, “These findings provide compelling evidence that PYY is a physiologically relevant regulator of food intake and body weight.”
                                                  Statistics show that diets have shifted from being more protein-rich to more carbohydrate-rich. The average Western diet now derives 49 percent of its calories from carbohydrates, 35 percent from fat, and 16 percent from protein.
                                                    If people in Western countries have been eating increasing amounts of carbohydrates, which do not curb appetite as well as protein does, the UCL team’s findings could help explain the obesity epidemic in North America and Europe.
                                                      Of course, the results of the two small clinical trials from Italy and Britain are not proof that high-protein, low-carb diets offer a panacea. As Dr. Batterham said of her team's work, “This research suggests that an increase in the protein content of the diet may help tackle obesity. However, large scale clinical trials are needed before high- protein low-fat diets can be recommended.”
                                                        Still, it makes sense to act on the available evidence, which suggests that diets low in carbs (bread, pasta, pastries) and rich in fish, fruits, nuts, beans, and colorful veggies (with modest amounts of whole grains) can help keep waistlines in control and discourage cancer and the major degenerative diseases.

                                                          Sources
                                                          • Fontani G, Corradeschi F, Felici A, Alfatti F, Bugarini R, Fiaschi AI, Cerretani D, Montorfano G, Rizzo AM, Berra B. Blood profiles, body fat and mood state in healthy subjects on different diets supplemented with Omega-3 polyunsaturated fatty acids. Eur J Clin Invest. 2005 Aug;35(8):499-507.
                                                          • Batterham RL, Heffron H, Kapoor S, Chivers JE, Chandarana K, Herzog H, Le Roux CW, Thomas EL, Bell JD, Withers DJ. Critical role for peptide YY in protein-mediated satiation and body-weight regulation.Cell Metab. 2006 Sep;4(3):223-33.
                                                          • Mithieux G, Misery P, Magnan C, Pillot B, Gautier-Stein A, Bernard C, Rajas F, Zitoun C. Portal sensing of intestinal gluconeogenesis is a mechanistic link in the diminution of food intake induced by diet protein. Cell Metab. 2005 Nov;2(5):321-9.
                                                          • Gevrey JC, Malapel M, Philippe J, Mithieux G, Chayvialle JA, Abello J, Cordier-Bussat M. Protein hydrolysates stimulate proglucagon gene transcription in intestinal endocrine cells via two elements related to cyclic AMP response element. Diabetologia. 2004 May;47(5):926-36. Epub 2004 Apr 14.
                                                          • le Roux CW, Batterham RL, Aylwin SJ, Patterson M, Borg CM, Wynne KJ, Kent A, Vincent RP, Gardiner J, Ghatei MA, Bloom SR. Attenuated peptide YY release in obese subjects is associated with reduced satiety. Endocrinology. 2006 Jan;147(1):3-8. Epub 2005 Sep 15.
                                                          • Batterham RL, Cohen MA, Ellis SM, Le Roux CW, Withers DJ, Frost GS, Ghatei MA, Bloom SR. Inhibition of food intake in obese subjects by peptide YY3-36. N Engl J Med. 2003 Sep 4;349(10):941-8.
                                                          • Small CJ, Bloom SR. Gut hormones as peripheral anti obesity targets. Curr Drug Targets CNS Neurol Disord. 2004 Oct;3(5):379-88. Review.
                                                          • Batterham RL, Bloom SR. The gut hormone peptide YY regulates appetite. Ann N Y Acad Sci. 2003 Jun;994:162-8.
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