• Amanda Dennis, CHNC, MPH

Diet Change Side Effects - Too much, too soon?

Updated: Nov 8, 2019

Many of us have experienced it. We decide to get on track with our diet and jump in with both feet. Some land strong and feel better right off the bat, while many of us stumble off the starting line and may end up feeling worse than we did before we started. This is often the case with drastic dietary changes, which can result in headaches, fatigue, irritability, bloating and gas.

Why is this?

Our bodies are extremely adaptable. This means that when our diet is less than ideal, our body adapts to best deal with what it’s given. This is a blessing, but these adaptations do not occur overnight. The body needs time to adjust to our changing lifestyle. As we’ve often carried less-than-ideal habits for long periods of time, it can take an extended period of time to adapt to new ways of eating.

For example, let’s look at the aptly named SAD diet, or Standard American Diet. This diet is characterized by a high intake of:

  • refined carbohydrates

  • red meat

  • dairy products

  • fried and processed foods

  • saturated animal fats and trans fats

  • preservatives and food additives

The SAD diet is also associated with a low intake of:

  • plant foods, particularly raw fruits and vegetables

  • whole grains

  • whole, raw nuts and seeds

On a long-term SAD diet, our body is often overfed, yet undernourished. This style of eating is calorically dense while lacking in the essential micronutrients and phytonutrients needed for good health.

The way we eat the majority of the time contributes to digestive and microbiome adaptations that best accommodate our diet. On a SAD diet, the digestive system and microbiome adapt to best deal with the abundance of refined grains, sugars, dairy products and animal fats present. For example, the gut environment of an individual consuming a SAD diet may adapt to include more protein-degrading microbes and fewer microbes adept at digesting starches and complex carbohydrates (Shankar et al., 2017).

When we decide to make positive changes to our diet, it often involves decreasing our intake of trans and saturated fats and red meat, and increasing our intake of fruits, vegetables and overall fiber. This is indeed a positive change, as diets higher in fresh fruits, vegetables and fiber are associated with lower rates of cardiovascular and metabolic diseases. However, our gut environment is still adapted to our previous diet and the shift to a more healthy microbiome does not occur overnight. This can lead to a few bumps in the road when switching to a new diet. You may feel heavy after starch-heavy meals and may experience gas and bloating while your microbiome shifts to include more microorganisms that thrive off of these new foods. The bacteria that help break down meat are not necessarily the same as the bacteria that efficiently break down starch. While our body can still digest these new foods, it may produce some nasty by-products in the process (i.e. gas).

Shifting away from addictive foods such as refined carbohydrates and caffeine can also leave the body in a state of panic once these addictive substances are removed. While a positive change overall, it can lead to symptoms of withdrawal such as headaches, moodiness and irritability. Once our digestive system and microbiome adjust, however, you can begin feeling the benefits of this new change in lifestyle. A healthy microbiome is associated with elevated mood, better resiliency to stress and anxiety, increased energy and improved digestion. In other words, you'll feel better than ever!

So, what can we do to make this transition as smooth as possible? Some of us are all-or-nothing types of people. For those of you who fall into that category, I would recommend the following tips to ease intestinal distress when making drastic dietary changes:

  • Take a digestive enzyme supplement with meals to support healthy digestion

  • Soak whole grains, seeds and legumes in water overnight to reduce the presence of enzyme inhibitors that can impair digestion, as well as anti-nutrients such as phytic acid and lectins, which can reduce the absorption of vitamins and minerals

  • Take a daily probiotic to help populate your gut with helpful microorganisms, and include probiotic-rich foods in your diet (traditionally-made sauerkraut, kimchi, kefir, tempeh)

  • Get moving! Exercise can help relieve bloating and stimulate intestinal motility.

  • Consume herbal teas such as peppermint and chamomile, which can ease stomach and intestinal distress

Otherwise, try to opt for more gradual changes in diet. Focus on adding nutritious, whole foods first and increasing fiber gradually. Once you feel adjusted to the addition of these foods, begin to remove those that no longer serve your health goals. This can help ease the transition into a healthier diet, and help increases chances of success.

Note: If a significant change in diet is causing a serious reaction, or pain beyond simple discomfort, discontinue and consult a physician.


Shankar V, Gouda M, Moncivaiz J, Gordon A, Reo NV, Hussein L, Paliy O. 2017. Differences in gut metabolites and microbial composition and functions between Egyptian and U.S. children are consistent with their diets. mSystems 2:e00169-16. 10.1128/mSystems.00169-16

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